一个多月前，我们发布了第一篇关于《自制口罩的最佳材质》数据的文章。现在美国疾病控制与预防中心建议每个人都应该戴上口罩，这就引起了一场自制口罩的全球运动。
《自制口罩的最佳材质》这篇文章（浏览量超过1000万次！），是关于口罩材料测试的一次初探，但数据并不完整。
所以在过去几周里，我们一直在努力测试一些之前遗漏的、和被大家询问多次的材料。从咖啡滤纸和床单，到可重复使用的无纺布购物袋、法兰绒和Scott蓝色纸抹布，我们都做了测试。
而且我们的同事还提出了自制口罩需要注意的问题，比如材料的透气度。让我们直接看看数据吧。
我们选了哪些新的自制口罩材质?
在本次测试中，我们总共测试了30种新材料，是剑桥研究中测试种类的三倍。
我们在众筹平台上开启了投票，根据大家投票出的材料结果进行测试，如果你们有想要了解的材料，还是可以告诉我们！我们会继续做测试，不断分享更新的数据。
自制口罩测试步骤
我们模仿了剑桥大学研究者们使用的亨德森装置。在我们的设备中，左边放一个风扇，把空气和颗粒吹过右边的自制口罩材质。
在自制口罩材料的另一边，用Met One GT-521颗粒计数器测量透过口罩材料的颗粒数量。我们测试了比较大的1微米颗粒，约是埃博拉病毒的大小；和比较小的0.3微米颗粒，大约是天花病毒的大小。而COVID-19冠状病毒本身是0.06-0.14微米，在水中是5-10微米大小。
通常来说，0.3微米是最难过滤的颗粒大小，所以我们把0.3微米作为测试标准，然后保守给出每种材料的测试数据。测试方法的细节都是公开的，可以在我们的文章《DIY口罩材质测试的补充数据》里看到。
自制口罩测试结果：埃博拉病毒大小的颗粒（1微米）
对于埃博拉病毒大小的颗粒，N95口罩、医用外科口罩和HEPA滤网的过滤效果最好，可以过滤超过99%的1.0微米及以上的颗粒。其次，HERO咖啡滤纸过滤了98%的颗粒，厨房纸巾、帆布、牛仔布和纯棉床单也都在90%以上。
虽然有些材料的过滤效果不太好，但至少都能过滤50%以上的颗粒。效果最差的四种面料分别是羊毛围巾、涤纶围脖、棉质头巾和浅色围巾。
自制口罩测试结果：天花病毒大小的颗粒（0.3微米）
对于0.3微米的颗粒，这些材质的过滤效果便大不相同。N95口罩、HEPA滤网和外科口罩的过滤效果依然是最好的，其过滤效率都超过了75%。但是，这些材料在捕捉小颗粒时，始终比捕捉大颗粒要少。
在家用材料中，HERO咖啡滤纸排在第二名，过滤了62%的颗粒。但只有四种材质的过滤效果超过了48%：40D尼龙、CHEMEX咖啡滤纸、厨房纸巾和帆布。
而另一些材料的效果就有点惨不忍睹：头巾、围脖、围巾、除尘布和纯棉T恤的过滤效果都不到10%。
规格的问题
在此特别说明一下纯棉T恤。因为剑桥大学的研究人员推荐纯棉T恤是自制口罩最好的材料之一，但在我们的测试中，它只过滤了3.4%的0.3微米颗粒，而双层纯棉T恤过滤了15%的颗粒。
我们怀疑这是因为T恤的材质有所不同，我们测试的材质更为轻薄。制作口罩，材料的重量和厚度都是影响结果的重要因素。
这种自制口罩的材料最差！
我们测试的三条围巾，都过滤了不到10%的小颗粒。效果最差的是100%的苎麻（类似亚麻）围巾，只过滤了2.8%。
美国总统特朗普建议用围巾来做口罩，但数据显示，围巾在过滤病毒颗粒方面是最差的。
天然纤维比合成纤维好！
从这些数据中我们得到了一个非常重要的信息，天然纤维（比如棉和纸）通常比合成纤维（比如涤纶和聚丙烯）的过滤效果更好。
合成纤维比较光滑、均匀，而天然纤维就比较粗糙、不规则。
天然纤维的不规则性似乎帮助了它更好的通过布朗运动（Brownian motion）捕捉微小颗粒。
最好的过滤材料，却不是最好的口罩材料
根据这些数据，咖啡滤纸和尼龙布是自制口罩的最佳材料。但是我们更推荐使用纸巾、牛仔布(10盎司)和纯棉床单（120支）。
为什么呢？因为当Smart Air的工程师Paddy把咖啡滤纸和尼龙床单放到嘴边时，他发现自己几乎没办法呼吸。也就是说，在选择口罩材料时，透气性是非常重要的。
这些自制口罩材料的透气性好吗？
为了测量每一种材料的透气性，我们记录了将一定量空气吹过每种材料所需的风扇功率。你可以把它想象成你的肺要通过这些材料呼吸，需要付出的力量。下面是测试结果：
很遗憾，大多数擅长过滤颗粒的材质，同时也是最不透气的。确实，一张非常厚实的咖啡滤纸可以有效过滤颗粒物，但它同时也不会让太多空气通过。
两层100%纯棉T恤、内衣垫、70D尼龙、擦手纸巾、棉质床单（120支）、牛仔布（10盎司)，它们的透气效果都在医用外科口罩和N95口罩之间。
透气性和过滤效果：自制口罩的最佳组合
衡量透气性和过滤效果，我们建议下面三种材质：
- 厨房纸巾
- 牛仔布（10盎司）
- 100%纯棉床单（80-120支）
内衣垫的效果相当不错，过滤了14%的0.3微米颗粒和76%的1.0微米颗粒。虽然男士们应该不好意思在公众场合把它戴在脸上，但不得不说它的确是一种又奇特又有效的口罩材料。
0.4-0.5毫米厚的帆布，比外科口罩、甚至纯棉T恤的透气性更好。
但是，如果你家里没有更厚的布料，我们的数据表示，双层纯棉T恤依然是自制口罩不错的选择。
如何找到最好的面料：最便宜的测试方法
对于我们的数据还有一个问题，T恤和床单的材质是不同的，有厚有薄。如何保证你家的材料和我们测试的一样呢？
没有3000美元的激光颗粒计数器，这里有一个简便的方法：尝试“最便宜的测试”。
- 把你的材料拿到阳光下
- 看有多少光能穿透它
- 把它和这张图进行比较，来评估材料的效果
划重点：自制口罩的终极材料
像咖啡滤纸这样的材料在过滤较小颗粒方面表现得非常好，但它的透气性不佳，不适合做成口罩。那考量到透气性和过滤效果这两个要求，自制口罩的最佳材料是：
- 牛仔布(10盎司)
- 床单(80-120支)
- 纸巾
- 帆布(0.4 -0.5毫米厚)
- Scott蓝色纸抹布
资助声明&感谢支持公开测试数据的人们
我们做的测试都是无偿的。作为一家社会企业，Smart Air的社会使命是提供给大家方便获取的信息和工具，保护人们免受空气污染的的危害。我们这样做不是为了赚钱，而是为了帮助我们所生活的社会。
从西班牙到越南都有支持我们公开数据测试的人们。这些善良的人们包括：Joni，一个患有肺部疾病的残疾老兵；还有在美国Rochester的K. Sue，她把对我们的捐款当做她70岁的生日礼物。
如果你想帮助、支持我们测试更多材料，可以查看我们的活动 : https://fundly.com/best-diy-mask-materials
P.S. 10盎司的牛仔布是什么?
牛仔布通常用每平方盎司的重量来衡量，也就是每平方码的克重。一平方码10盎司的牛仔布约重340克。牛仔面料被分为轻型、中型和重型，低于12盎司的牛仔裤是“轻型”的，所以你可以把我们测试的10盎司牛仔裤想象成轻型的牛仔裤。
I’m looking for data that would compare fitted vs unfitted face covering for the best house matérial and the surgical mask. Thank for your efforts and this informative article
Right from the start I kept reading that polypropylene was the best so that’s what I’ve been making, but I keep finding other studies that use other materials, why is polypropylene not mentioned or studied more ?♀️
Hi. I make masks and have a question.
Basically, I have a three layer design. 9-10oz Duck canvas/4oz raw natural silk noil/polyester spandex chiffon.
One study , the ASC Nano one, showed two layers of polyester spandex chiffon or natural silk as effective at catching small particles.
However, you’re research does not appear to show the same. Why? You’re research puts the polyester spandex kinda low on the performance chart. But you’re testing an athletic shirt, not chiffon.
The other research suggested the chiffon outperforms natural silk slightly so I’ve considered just canvas/chiffon/chiffon and basically dropping the raw silk.
But does having three separate materials have a broader spectrum of protection?
I’ve made well over 300 masks so far and would like to refine them. Can I pay to have a few tested?
For display only
https://adamsworkshop.wixsite.com/mysite?page=2
Hi Adam. Song here from Smart Air. Nice try on DIY masks! We do offer mask testing services. Please contact [email protected] with more detailed requirements.
Hi Paddy
This seems to assume you breathe “through” the mask. Many people breathe around the edges since most masks are not a close fit.
Breathing “in” may mean people tend to breathe through the mask, as it is sucked to their faces. Breathing out tends to blow the mask away, so air can escape around the edges; especially when people cough or sneeze. Since the main reason for wearing masks is to reduce the spread from infected people, masks with a soft cotton wool lining pad might be best…it may act both as an absorber and as a seal.
What about 180 tpi batik fabric? I’m trying to find information and can’t.
Hi – Wow, you guys are awesome! I’m preparing to send my child to school. We are trying out many different reusable cloth masks (and holding them up to light). Now, I’m trying to decipher the best (and safest!) filters to put in them. What do you recommend that works but is also surely safe to breathe in?
Thanks!
I’ve been prototyping masks since sometime in March. The best center filter material I’vee found is the “filti” nanofiber filter material.
Patrick Moran,
I’m excited to see that you guys have finally been able to get a sample and test the filti filter fabric material.
My question is… Since you say that it is “the best center filter material” that you have found… why is it not on any of the lists you guys are posting about best DIY materials? Where would it fall on the chart that lists the “Best Materials for Homemade DIY Face Masks?”
I’m a little confused. Thank you!
I’m a DIY mask maker in the USA. One published source in the USA published evaluations of combinations of materials measured. At the top of their raw evaluations:
1 layer Filti+ 1 layer 6.5g Cotton Rip Stop 84.03% 13.33
2 layers Kona 100% Cotton + 1 layer 1500 Filtrete Furnace Filter 80.85% 8.1
They then factored in breathability:
2 layers Kona 100% Cotton + 1 layer 1500 Filtrete Furnace Filter 72.7
1 layer Filti+ 1 layer 6.5g Cotton Rip Stop 70.7
I’ve never heard of rip-stop cotton, and I’ve been making camping equipment with ripstop nylon for fifty years or so.
I have no idea why they would not sandwich the Filti non-woven nano fiber material between two layers of something breathable but of a tight enough weave to serve as a pre-filter to take out dust. I found one “batik” material, a cotton fabric of 0.63 pounds/square yard, that I like. In the USA there is one outlet https://www.flyingbulldogs.com/fabric-yarn/ that gives the weight/square yard and the fabric material for everything they sell.
They called one of my favorite materials “cotton,” and they were wrong simply because the manufacturer didn’t give the right info. It’s your best shot at finding things like medium weight canvas and being sure you know what you are getting. Any of their 0.5 lb/sq yd cotton quilting materials (AKA batiks by some people even though they have nothing to do with Indonesia) would be my preference to a “ripstop” unless I had a chance to dissect that rare bird.
We use 3 layers… Woven cotton outer (around medium weight) filter layer of cotton or cotton & bamboo wadding and a liner of soft cotton t-shirting. Quite breathable, very comfortable and seems to do a decent job of filtering – though I’d love to run a more sophisticated test on them.
I started making face masks at the end of March. At that point the recommendation was that the material should be tightly woven and if held up to the light should not allow visibility. So two layers cotton and an inner layer of calico. About 80 made and given away so far…
But if the mask is impervious, the air (with viruses) will leak around the edges of the mask; the air has to go somewhere.
Great article, but the graphics (efficiency bar charts) are nearly unreadable. Black font is better than gray and why is the font like 1/2 of the text font size? Thought I’d click on it and it would get big but nope. Thanks.
Nice article! Thanks for running the tests on mask materials!
I’m wondering if you have tested any of the Pellon nonwoven fusible products, or if you could consider that for a future test. This has been recommended by some sewing sites as a permanent filter layer for home-sewn masks. It can be fused (by ironing) to either the inner or outer cotton layer of the mask, and can be laundered. I’ve made some masks with this, and for breathabilty, prefer the lighter weight Pellon (for example, Pellon 911FF Fusible Featherweight, or Pellon 950F ShirTailor Fusible Interfacing 20” White). These can be found at fabric stores such as Joann Fabrics. It would be good how well it performs in your test, especially after laundering a few times!
Are you sure it was *fusible* interfacing that was recommended in your sources? I have only seen non-fusible (sew-in) non-woven interfacing recommended by officials/public health services sites. I believe the reasoning being that fusible material is too occlusive.
Thank you for your research. Is there a way to get a larger copy of the 1 micron graph please? Thank you.
Paddy here is a link to the Filti Material Data Sheet.
https://filti.com/app/uploads/2020/04/Filti-Face-Mask-Material-Data-Sheet-040920-1.pdf
Paddy, Liz,
I just spoke to a representative at Filti Fabric. You can email them and ask for a free sample. Tell them who you are and why you are requesting the sample. i.e. Tell them that you want it for testing purposes and that your website publishes the information online and shares with its users. Their email is [email protected]
I would love to see the results of your test. If not please send me the address and I can send you one of the filters that I have already cut. They are shaped in basically a semicircle I hope this helps.
Stay Safe!
Karyn
Dear Paddy,
Have you done any tests using the Filti nanofiber fabric that is now available?
The spec sheet shows a MERV rating of 16 . It is comprised of 3 layers of lightweight composite filter media. It is constructed from polypropylene spunbond nonwoven with a nanofiber fine filtration layer, surface layer of polyester nonwoven. The Material Data Sheet states that it is highly efficient (up to 95%) on sub micron particles, including bacteria & viruses.
I would be interested to hear what your evaluation of this product is Thank you!
Hi Karyn, Liz here. We haven’t tested the Filti material yet. A couple of people had been asking us but we do not have it here available in China. If you have a spare one and willingly to ship a sample to us, we can help to test it.
Liz, how big a piece of fabric do you need? I have cut filters out of most of my fabric and only have scraps left. But if you provide me an address I can try sending something. Thanks. Stay Safe! Karyn
What if we used a disposable mask inside a pocket as a filter (without cutting it as you noted that would degrade the seal). Would that be a viable option?
Also is it dangerous to spray a reusable cotton mask lightly with lysol in between uses, as long as I air it out for 24-48 hours between uses, and wash the cotton once a week, or every 3-4 wearings multiple days apart? Thank you!
I only had one N95 in the beginning so I had to reuse it. I knew enough not to wash it. But, I did spray it a few times and let it air dry for a few days between wearings. Was that really stupid? as in dangerous? LOL! Thank you!
I just spoke to a representative at Filti Fabric. You can email them and ask for a free sample. Tell them who you are and why you are requesting the sample. i.e. Tell them that you want it for testing purposes and that your website publishes the information online and shares with its users. Their email is [email protected]
I would love to see the results of your test. If not please send me the address and I can send you one of the filters that I have already cut. They are shaped in basically a semicircle I hope this helps.
Stay Safe!
Karyn
Hello,
I purchased several neck gaiters/buffs early on in the pandemic. I see from here that they are not the greatest at filtering out exhalations. I do see that paper towels or denim squares are ideal for mask materials, so would it be okay to use a neck gaiter, put a square of towel/denim over the nose and mouth region, then pull the lower part of the gaiter back up over it to keep it in place? So it would be gaiter/fabric/gaiter.
Hi Steve, Liz here. We haven’t tested a neck gaiter yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials for making a DIY mask, I suggest to use the materials we already have data on for now. Just make sure it seals well. If you just pull up the gaiter, it can still leave a gap at your nose area.
I’ve seen articles noting pantyhose placed over disposable masks helped close the gaps and therefore increasing the effectiveness of the disposables. I would think, instead of using pantyhose, you could use a snug fit gaiter (that outlines your face features) over a mask in the same way. (if using a disposable mask I would put it on first using the ear loops then just pull up the gaiter over it, instead of 2 ply as you mentioned). I would think this should be workable for any filtration media (whether the denim or towels, etc). You might need to experiment with the shape, though, as a square might not be adequate for complete coverage of the nose and mouth. You might need to do more of an expanded oval or rounded triangle. Just a thought!
hey, Paddy. Great information right there, thank you so much. I was wondering, what are your thoughts regarding a DIY denim mask WITH a homemade activated carbon (or charcoal) filter? I’ve purchased some from my nearest aquarium and made an additional filter for the mask. I’m a biochemist, so I remembered its amazing filtration capabilities. What do you think?
Hi Daniela, Liz here. Using an activated carbon filter would be an effective way to filter out VOCs. However, I suppose you want to make the DIY mask protecting you from the Covid virus? If so, you need a filter that can filter out particulate pollutants.
After searching the web, I cannot find anyone talking about using a surgical mask as a filter. I have several store bought cloth masks with a pocket in which a filter can be inserted. A surgical mask stretched out and cut in half fits perfectly.
My thought process is that one would have the benefit of the meltblown fabric for filtration and the tighter fit provided by the cloth mask.
Am I missing something, or is this a viable option?
Hi Mary， Liz here. The filtration rate for a surgical mask can be real good for a daily protection. If you have a surgical mask, you can just wear it instead of using it as a filter. Cutting it into half will damage the seal around the layers thus weaken the filtration efficiency.
I do this. But, I put on my disposable mask first in the normal way and add my cloth mask on top of it. I have also cut some to size to insert in the filter pocket and with the tight fit, I feel like the disposable layers are held together enough to work well. I suppose I could always melt seal the edges or perhaps tape or hot glue them.
100% cotton quilting fabric and broadcloth tightly woven dress shirt materials—have you tested those? Makers are promoting their use backed with nonwoven polyester interfacing.
Hi Charlene, we haven’t tested broadcloth tightly woven dress shirt materials yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
Dear Paddy,
I greatly appreciate your clear, well-presented research.
Based on this assessment, HEPA filters score well on filtering virus-sized particles and score well on breathability. Yet they are not on the recommended list. Is that because of cost and availability?
I have made some HEPA filter masks using Miele GN HyClean 3D Efficiency HEPA filter vacuum cleaner bags (bought at Harvey Norman). These are essentially square, with the hole more or less in the middle. When pressed flat, I have used a Wellcare (by tempo) KN95 mask (from Bunnings hardware) as a template and can cut a mask from each of the four corners of each HEPA filter bag.
I add a 13cm sleeve on top and inset a 12cm length of a florist wire for shaping over the nose and add 2x 20cm elastic ear loops. The resulting masks have a vertical factory join with no needle holes. The only sewing needed is for the sleeve for the wire and for the elastics. I sew both of these with a single seam around the outside. It takes me less than 10 minutes to cut and make each mask. I expect this could be reduced by making several at one time.
The only slightly tricky bit is aligning the template so that the nose side is on the sides of the vac bag rather than the top or bottom, because the side factory seams are more easily foldable for adding the sleeve for the nose-wire, which crosses the factory seam.
I first made HEPA filter masks based on this YouTube video: https://www.youtube.com/watch?v=W6d3twpHwis&t=3s. But these were more work and more time-consuming to make and made less use of factory seams – so have more needle holes.
I am interested to hear your thoughts on this.
Regards,
Bob Cumming, Melbourne, Australia
Hi, Bob, Liz here. The only reason that we are not recommending HEPA filter is that different manufacturers may have different standard on production. All HEPA filter should fit the standard for filtering air but are they all suitable for filtering breathing air that close to your nose and mouth? We are not sure about that, so we didn’t recommend it in the article. Personally, if there is no way I can get a reliable surgical or N95 (or equally standard) mask but I have to go to the hospital for a visit, I would choose to make my DIY mask using a HEPA filter instead of a cotton t-shirt for it’s better filtration efficiency. But will I use it as a daily protection when I’m going out? I probably would pick the cotton mask instead. Hope this answers your question!
Thank you for your well- researched and comprehensive information! Knowing the breathability and fit as well as the filtration efficiency of mask materials allows me to make an informed decision on the type and material of the mask I wear.
Which side of the 2.5 filters should face outward? I am making cloth masks with filter pockets.
Hi Diana, Liz here. If you use the filter resembling to a HEPA filter, the fluffy part should be facing outside while the smooth side facing your mouth.
Here are two journal articles of interest:
“Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks” https://doi.org/10.1021/acsnano.0c03252
“Household Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric Charging” https://doi.org/10.1021/acs.nanolett.0c02211
Multiple layers were tested together, and the second article specifically covers polypropylene as used in interfacing. The difference between melt-blown (used in medical masks) and spun-bond (used in interfacing) is clear. The spun-bond interfacing doesn’t have the dense fractal structure of naural fibers or melt-blown fabrics. So interfacing is not likely to be much help in masks based on physical filtration.
However, there is also good data on the electrostatic properties of fabrics. While cotton fabrics (and plant-based fibers in general) do not readily hold a charge, animal fibers, synthetics, and silk can all hold a charge and this helps to protect against the smallest particles, as documented in this article. I plan to add an inner lining of fine-weight silk (since I happen to have some) between two cotton layers (one soft knit, one quilting cotton), with the bottom seam open, and charge it by rubbing with a scrap of latex or plastic before wearing. This is where the synthetic interfacing might also be used.
Finally, the issue of mask fit is another major issue if masks are to provide maximum protection. This article explains that a strip of stocking worn over nearly any mask improves the fit and the protection: https://www.npr.org/sections/goatsandsoda/2020/04/22/840146830/adding-a-nylon-stocking-layer-could-boost-protection-from-cloth-masks-study-find
Again, a nylon layer could be charged by rubbing and this would also improve the protective level.
Dear Paddy, You have done great job. I wish that you test Nano fibre base filters ,which will become available very soon at cost effective price.
If they are in comparrision then one better knows about the breathability abd efficiancy one can get.
If you wish I can supply you the filter equivalent to N95 and N99.
Thank you so much for this info. I’ve gone to this website numerous times. I’ve seen several mask tutorials online that show people sewing interfacing as a filter layer for their reusable DIY masks, but I haven’t seen anything about its effectiveness. I know Pellon makes one that’s 37gsm (Pellon 907 interfacing), but it’s Polyester, not polypropylene. If it’s effective, there’s also the question as to how long-lasting its effectiveness will be if it’s washed repeatedly. Anyone have any thoughts? Thanks.
A correction for my question above: the Pellon interfacing that’s 37gsm is Pellon 905 (907 was a typo).
And a follow up question: If the gsm is the same, does it matter what the material is? For example, is a 50gsm polyester/viscose blend as effective as 50gsm 100% polyester or 100% polypropylene? Thanks.
What about the PM 2.5 filters that go inside homemade and some independent manufactured masks. How effective are those ??
Hi Mary, Liz here. PM2.5 filters should be some type of HEPA filters, we do have a HEPA filter filtration efficiency tested that it can filter out 83% 0.3 (or below) microns particles. So I’d say it would be effective. The only reason we are being conservative on HEPA filter is we cannot be sure that whether the manufacturer making the HEPA filter making it safe enough as something to filter out breathing air so close to your nose and mouth.
isn’t the size of covid-19 closer to 0.125 micron versus your sizing test at 1.0 micron? also don’t ALL masks requires a fit test and real beards prevent this?
Hi J G, Liz here. We’ve tested both 1.0 microns and 0.3 microns. For the covid which is smaller than 0.3 micron, here is an article explaining why the 0.3 microns filtration rate can be used as a critical threshold: https://smartairfilters.com/en/blog/what-is-hepa-filter-how-hepa-filter-work/
About the fit test, some standard like N95 has the requirement but do not. Here is an article explaining this: https://smartairfilters.com/en/blog/comparison-mask-standards-rating-effectiveness/
If HEPA material that captures 80+% of .03 microns AND is easier to breath than surgical mask, seem that HEPA material would be the 2nd best choice after N95 material. Better than canvas.
3M A/C filter material rated at MPR 1500 or higher is near or equal to the 3M N95 material if double layered inside any mask used to hold on the face. Better if used behind a surgical mask or other better fitting designed mask than a surgical mask. Basically used the 3M material rather than PM 2.5 filters.
Hi Kent. Song here. Yes, HEPA filter performs well. The only reason we are being conservative on HEPA filter is we cannot be sure that whether the manufacturer making the HEPA filter making it safe enough as something to filter out breathing air so close to your nose and mouth.
Great article. So I have a mask (reusable) and it has a pocket for a filter. Assume that if the filter that you are recommending is washable (for example bed sheets) – I can wash that filter, the same way I do for my mask. Let me know if this is correct
Hi Ann. Song here. Good question! Data shows that washing N95 masks severely affects their performance. Here’s our data showing that you shouldn’t wash them: https://smartairfilters.com/en/blog/washing-masks-effective-virus/.
The best way we found to disinfect masks is to leave them out to dry..
Maybe you can wash your reusable mask and dry/change your filter.
Your reply to,Amanda said “ the filtration rate of kitchen paper towel is not likely as high as filter specifically designed for using in a mask.” So, what filters are specifically designed for a DIY mask? Vacuum cleaner filters, furnace filters, and even air purifier filters are not “specifically” made for DIY masks. I’m confused as to what you are referring to by “filters designed for masks.” Were you referring to filter material used for professional use as in N95 masks? I need to know what is recommend filter material for DIY masks. Can you clarify?
Thank you!
Hi Mitzi, Liz here. To clarify the answer, by saying “filters designed for masks” I mean some mask manufactures have mask models that with inserted filters. Those filters should be sanitized properly and pass test on breathability and filtration efficiency. Different manufactures should have different filters. For DIY masks, I mean if you have difficulties in getting a mask product and decide to make your own. So all of our tests are done with materials easy to get from home or your local grocery store.
Fantastic work you’re doing! Thank you! I wonder if you could find some sort of a measure of surface area in a fabric and test the effect of that. For example, for a piece of fabric of a given size or weight, low thread count cotton would have the lowest surface area, high thread count would have more surface area, and flannel or a terry towel fabric would have much more. I could imagine that this surface exposed to air could be one of the most important factors in filtration efficiency.
Great thoughts! I share your intuition. Having a larger surface area makes it easier to breathe in a mask. I wonder if we could build in some sort of “guide wire” or scaffolding that could allow the mask to occupy a larger surface area.
I think structurally increasing the surface area is an excellent and potentially easy to implement idea! I have thought a bit more and have three further ideas on this.
Firstly, in seersucker fabric small-scale ripples are introduced through slack-tension weaving. That would increase the area a little bit, but not to much.
Secondly, are you familiar with nuno felting? In this, a sandwich is created with a nonshrinkable fabric in the middle (usually cotton or silk), encased on one or both sides by a (shrinkable) thin layer of loose wool fibres. Through mechanical agitation the wool fibres entangle with each other and with the nonshrinkable fabric. Through a process called fulling the wool fibres shrink and pull the nonshrinkable fabric into lots of random, small-scale folds.
Thirdly, there is a sewing / embroidery technique called smocking, which locks flat fabric into lamellar conformations of relatively easily controllable density. Although I know this as a hand-sewing technique, I think I have seen it in bough garments, too. So there must be a machine out there that can do this.
Hope this helps a bit with your R&D!
I read that tea towels were good, but these haven’t been included in your test above, are these not recommended?
Hi, Courtney, yes, tea towels should work, and we have an article listed out the filtration rate of tea towel here:https://smartairfilters.com/en/blog/best-materials-make-diy-masks-virus/
That’s why we didn’t test it again in this article. Also, tea towel material and quality can vary a lot, so we just tested other materials that we can have more detailed specs to share with our readers.
Thank you! I’m very appreciative of all your work and for writing this up. You’ve made it very easy to read and understand. I’ve been using a mask I made after many attempts, and I hope it does its job when I need to go out. It’s comfortable, so it never needs adjusting, the inside and outside layers are quilting (100%) cotton, and the inside is non-woven polypropylene. It also has a wire across the nose, from cheek to cheek for assured fit, elastic ear loops and a velcro tab at the back of my neck. When I breath it goes in and out the front of the mask, not at all from the sides. I’m asthmatic so breathablility is SO important. So far so good, unless it’s hot out, in which case I stay home 🙂 Stay safe!
Are “Kitchen Towels” cotton dish cloths (tea towels) or premium/thicker paper towels?
Would be interesting to measure how quickly paper towel filtration degrades from on/off tension/flexing of inhaling/exhaling and saturation from moisture in exhalation. May or may not be feasible for longer term use (a work shift 8-10hrs vs grocery trip 1hr)
hi Keith, kitchen towels here refers to the tall roll paper towel we used to clean the kitchen oil or stains, like this one: https://www.gompels.co.uk/soclean-kitchen-towels-24-pack.html
Hope this clarifies things:)
Great info!! What are you using for “canvas”? Slacks? Thanks for explaining denim weight as light weight jeans!
We purchased varying thicknesses of canvas from a DIY shop, so it was just labelled as ‘canvas’. We didn’t cut up any of our existing items for these tests!
I am trying to figure out your “kitchen towel” and “paper towel for hand drying” terms. I am guessing it is due to country differences in what we call these things and not seeing a “full size product” photo.
Is the kitchen towel a paper towel with some quilting to it? If it is paper, is it single or double layer style?
Would your paper towel for hand drying be a brown, single layer, folded style substance?
Perhaps posting a full size product photo would help reach an even larger internal audience.
Hi Kathleen, Liz here. Kitchen towel are the tall roll paper towel we use in the kitchen to clean the water or oil stains. Like this one: https://www.amazon.com/Bounty-Quick-Size-Paper-Towels-Family/dp/B079VP6DH5/ref=sr_1_2?dchild=1&keywords=kitchen+towel+paper&qid=1591692295&sr=8-2
Paper towel for hand drying is like this one: https://www.amazon.com/Scott-Multi-Fold-Towels-Absorbency-Pockets/dp/B00M9ZI1TQ/ref=redir_mobile_desktop?ie=UTF8&aaxitk=hUwYImENVu46zha4qNo6gQ&hsa_cr_id=3606542720401&ref_=sbx_be_s_sparkle_mcd_asin_1
We used different brand but you get the idea 🙂
Hey folks, thanks so much for doing this work. I’m wondering about the combo of a denim mask + chemex coffee filter inside a filter pocket, which is one of the ones I use most frequently. How would this combo compare to, say, a surgical mask?
And in terms of the breathability question is this mainly about comfort or do effective but less breathable materials pose a safety concern? (I’m personally finding my denim mask + coffee filter combo pretty comfortable.)
Thanks!
Interestingthat you only use a 120 thread count sheet and you don’t say whether or not it is 100% cotton. I’m using some older 100% cotton sheets that are 900 thread count for a filter and nobody has any problem breathing through that.
Hi Catherine, the 120 thread count sheet is 100% cotton. And we picked 120 thread because lower thread count is more accessible and cheaper. Although we didn’t test all thread count choices, a higher thread count sheet would do better than the lower one.
The only material I noticed listed with two layers is the cotton t-shirt. So am I to assume that the 120ct 100% cotton bedsheet results listed in the table is for only one layer?
Hi Jessica, Liz here. Yes the bed sheet test is conducted with one layer of the fabric.
Hi – please could you advise me on the following filter question: Bearing in mind the combination of protection/affordability/availability of a mask and filters, what is your opinion on the effectiveness of using kitchen roll paper (which is of course easily available and cheap) as a filter within a mask, against purchasing PN2.5 filters – as recommended by ITV This Morning?
Hi Amanda, Liz here. We listed out the filtration rate of a kitchen paper towel which can filter out 48% 0.3 microns particles. Can you use it as a mask insertion? The answer is yes, but the filtration rate is likely not as high as a filter specifically designed for using in a mask.
Thank you so much for this information!
Thanks for testing a range of materials. There is a study out from Argonne National Lab that looked at the benefits of using 2 layers of different fabrics to achieve better results than just each fabric individually. Some of the fabrics that I would like to see tested as I have been using them and from my perspective as a chemist they make sense as good filter materials are 100% woven wool that has been washed hot and felted by washing and drying, polyester fleece (should hold a charge well), cotton flannel that has been washed hot, and linen as a liner material for the other materials suggested. I’m happy to send pieces of these fabrics if you guys are willing to test them.
Here is the link to the paper mentioned. https://pubs.acs.org/doi/abs/10.1021/acsnano.0c03252
Thanks for this question—I was looking through the comments before asking the same thing!
DIY – You can produce hundreds of HEPA masks by thermoforming plastic. All you need is a shop-vac, plaster of paris, an old toaster… Okay, it’s a little complicated but worth the effort: https://www.thingiverse.com/thing:4396982
Thanks for this, it is the first time I’ve felt confident about what to do. Making masks for the family with bed sheets and just wondered if it’s best to make masks with a pocket for kitchen paper encased within them (but removable) or, whether it is best to have the kitchen paper next to your face ??♀️
Thanks again, Deb
What type of HEPA filter was used for the test?
Hi, Alex, we used the HEPA filter for our Sqair. H11 grade. Our engineer just flatten the folded HEPA and tested the material in one piece.
What about Filti?
Read this full article: https://www.businessinsider.com/filti-mask-material-filters-particles-9-times-better-than-cotton-2020-4
Company site is at https://filti.com/product/filti-face-mask-material/
Also take a look at this site: https://www.sewcanshe.com/blog/face-mask-fabric-from-filti-product-review
Look at the image of a table of data on Filti a ways down on the page.
Filti is rated at MERV 16, N95 maps are MERV 12 or 13.I’m going to be trying this material in some mask designs – a couple of which are masks shaped pretty much as N95 masks – I’m goign to try plastic mesh – needle point stuff – to make a shaped base and then apply fabric with a pocket for a Filti filter insert or simply with one or two layers of Filti in the mask.
Note about filter inserts – you need to take every effort to make sure that the insert covers all of the mask so that you don’t have air leaks where the filter insert doesn’t cover all of the mask material.
I let N95 masks set for at least a week to dry them out and deactivate any virus particles. If these masks I’m working on turn out to be workable, the best practice would be to have seven masks and rotate them, putting a used mask in a paper bag for storage. Use paper bags so that the mask can dry out as the moisture goes out through the paper bag.
I have been making facemasks with a sewn in Hepa filter . If they are washed will it affect the filters performance?
Good question Romana! Data shows that washing HEPA filters severely affects their performance. Here’s our data showing that you shouldn’t wash HEPA filters.
I have acquired this same filti material. I expect it to be similar in effectiveness as the HEPA filter referenced here, but only if used for very short time. It won’t do to wash it. I use masks made with pockets for inserting this material. I dispose of this filtering material after very little use and machine wash my cotton masks after every use. I plan on making a few disposable masks with the filti material to have on hand.
I would like to point out that coffee filters are difficult to breath if you put them clote to face like a fabric. However, you use them like a cup (you showed bra cup example), then the breathability is not a problem. it is about available air mass around nose as opposed ot trying to force air through small holes in coffee filters (orifice in fluid mechanics term). We have been using coffee filter with great comfort so far (even kids). Here is DIY video of how to make such mask:
https://www.youtube.com/watch?v=ejGjBiwpLnQ .
You may also point out that disposable masks are safer than re-washable ones that is why professional safety masks like N-95s are always disposable type. Hope you include such info i the analysis. it would be not be wise to drop coffee filter just for breathability. A lot of people cant breath with even thin cloth when it is close to their nose.
What about the PM2.5 inserts for masks?
Hi Norman, Song here. PM2.5 filters should be some type of HEPA filters, we do have a HEPA filter filtration efficiency tested that it can filter out 83% 0.3 (or below) microns particles. So I’d say it would be effective. The only reason we are being conservative on HEPA filter is we cannot be sure that whether the manufacturer making the HEPA filter making it safe enough as something to filter out breathing air so close to your nose and mouth.
bamboo (paper) towels, nobody is talking about them, they are non woven, washable, under a microscope look a lot like furnace filter, all natural, absorbent, resists microbial build up.
“Denim is typically measured in weight per square ounce” Confusing!
Indeed, it took us a while to get our heard round this!
I assumed it was a typo, and should have read “measured in weight per square yard.”
Are all the results shown based on a single layer of the material? The replies to comments are now rather long to scroll through to find the answer. I am mostly interested in the denim fabric.
Hi Jennifer, yes, all tests are done with a single layer material.
Have you tested 100% Irish linen for masks? Regards
Hi Andy, Liz here. We haven’t tested that yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
I’ve found that an easy home test is trying to blow out a candle while wearing the mask. Most materials failed. I was able to blow out the candle easily.
I am making masks from a 1000 thread count sheet but up to now I have bought two lots of elastic. 5mm flat elastic which is too thick behind the ear, and secondly 3mm roll elastic which I am unable to join as it comes undone straight away… please, can anyone suggest what will be the best. Many thanks to you in advance.
Thanks for the info. My wife has just started making some masks for us with 100% cotton but it seems very thin. Thinner than some t-shirts and rigid. She did do two layers but I’m guessing we need a filter- she left spece. Would the recommended filter be papertowels that can be easily discarded and the masks washed? we’re thinking about denim from old jeans- would that need be doubled and still require a filter? Hepa filters seem hard to find. If anyone also has info on how to find canvas by .4mm thickness? Not finding it that way. would love links to where to find materials. THANKS
Is a higher thread count on bed sheets better as I can not find anything under 200
A higher threadcount will likely be even better at filtering, although you should check its breathability, Michael! Hold it to your mouth and try breathing. If it’s fairly difficult, then it might be uncomfortable to wear as a mask.
Thank you so much for all of this valuable information. It is greatly appreciated. I’m just now preparing to make a few masks, as I’m heading back to work shortly.
Thank you greatly for your work! Very helpful.
Hi, there was another study (https://medicalxpress.com/news/2020-04-homemade-masks-silk-cotton-boost.html) that included natural silks – for holding a static charge – and cotton flannels and cotton quilt with cotton-polyester batting, were giving very good results.
Have you tested these fabrics? Thank you.
As for masks patterns someone was asking below, I used the HK mask from a Dr. K Kwong, a doctor at the HKU Department of Chemistry, it’s Free (https://diymask.site/?fbclid=IwAR2VI7AuU5JhbvhKAOR7g7_W59eAnrpvGLBraU6emwa3n05fta7RUNHOTkI)
– It has a nose pincher too, I used a big twist tie that came with a heavy piece of equipment; some use garden metal ties; etc.
– It has a nice fit, no gaps around if you adjust for the wearer,
– they have pattern sizes for men, lady, teen, kids and instructions. I lengthen the lady’s size at the chin a bit. The men was good for my husband.
– they use two layers, I used 4, I made it: top shell 100% cotton / layer 2, 100% natural silk / layer 3, 100% cotton / layer 4 which is the flap for filter pocket 100% cotton, a bit of velcro to keep pocket closed at bottom of chin. Microbiologist Jason Tetro, more layers is better.
– Instead of leaving the top part of the mask open for the filter pocket like they do, I sewed it closed, our filter pocket opens only from the bottom in back.
– We wear them with 2 thickness of paper towel in the filter pocket, two layers has no light peeking through which offers better protection for everyone.
– The breath-ability is good.
– Make sure it goes just below chin, and pull taunt string tying for less gaps around the mask, ties either behind the ears, head (bottom of neck and top, or both.
Is it the best mask? I don’t know, but we’re satisfied.
I’m no expert, but I did talk to a friend PhD (bio-chemistry) in synthetic membranes who has 35yrs in research, and after seeing the fit (video) and asking me questions about the mask, he thought it might be a good mask. He recommended 2 layer paper towel after he had me look at the light to see if light came through with one layer, it did, but not with 2.
When breathing in, it feels like it pulls air through the fabric and not from the edges.
This is my experience with DIY face masks.
Thank you for this valuable info! Any comments on the mask frames printed in a 3D printer to better fit the fabric?
Quilters cotton and batik are good sources thank you for your work and please read up on that.
thank you
Hi it would have been easier if the fabrics were tested by weight. It is barely impossible to find any fabric by thickness or thread count. Thank you
Search 200 thread count pillowcases for fabric if you can’t find
Newer research than the Cambridge Study is available. You’re absolutely correct about natural fibers…. Fit is important too, though.
Short version here: https://www.sciencedaily.com/releases/2020/04/200424081648.htm
Long version here: Abhiteja Konda, Abhinav Prakash, Gregory A. Moss, Michael Schmoldt, Gregory D. Grant, Supratik Guha. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano, 2020; DOI: 10.1021/acsnano.0c03252
I’m using a mattress protector a filter in cotton mask.
What about muslin (cheese cloth)?
Single or doubled over
Hi Nina, we haven’t tested muslin yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
It keeps being stated that DIY masks are NOT meant for stopping you catching the a virus, they are meant to help stop YOU spreading it if you have it.
Better to do both
If your mask has the materials here they are recommending, You will have protection for yourself and others. It is also important that your mask fits securely to your face. Make sure you cover your nose as well.
How does ripstop nylon paired with broadcloth work? silk with broadcloth? thanks again
How about giving us a pattern or patterns to start with and then suggest the straps to attach to it?
https://members.sewitonline.com/wp-content/uploads/2020/03/How-To-Sew-A-Facemask-Instructions.pdf
I just did the light filter test, none coming through.
FYI: There’s a study by Abhiteja Konda, Abhinav Prakash, Gregory A. Moss and others called “Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks” which suggests that a combination of materials (one layer of the tighter-woven cotton plus two layers of silk, or two layers of chiffon for example) might be very effective due to a suggested combined effect of mechanical and electrostatic-based filtration.
I’ve read in the comments that you’re already planning a follow-up article with material combinations, so I’m looking forward to that!
(Personally I’m wondering if paper (kitchen paper towel or Tempo tissue paper) for mechanical filtration and silk or chiffon for electrostatic filtration might be an effective combination. Probably yes, If I understand the aforementioned study correctly, but more research is always welcome)
I’ve been using 2 layers of 300 thread count cotton bed sheet. Would be interested to see how the efficiency improves or otherwise as you go up the thread count. Easy to buy and can make loads from one sheet. Just hope it’s efficient…..
Thank you for this important work. Are PM2.5 filters useful to insert in cotton DIY face mask?
Hi Annabelle, I assume by PM2.5 filter you mean PP/PET material HEPA filter? If so, click here to see our knowledge base QA for the answer: https://smartairfilters.com/learn/smart-air-knowledge-base/can-flattened-hepa-filters-work-as-homemade-make-mask/
it is a carbon filter.
Hi there. Im working with a team of people in the UK making and supplying fabric masks. This information had been very useful. One material thats easy to get hold of but aren’t on your list is non-woven interfacing fabric. Called Pellon or Vilene as brand names. We have been using the heavy weight one as some says it might be a good filter option but there is no real data out there about this. It looks a bit like felt or a hoover bag. Would be amazing if you could test this fabric as it would help a lot of makers. Thanks Sibel
We’ll try and look into it, Sibel! We have a campaign here where you can stay up to date on our latest tests, as well as support us and vote on the materials you hope we can test: https://fundly.com/best-diy-mask-materials
Can someone explain how this converts to “nm”?
I was reading that the 1918 flu was 80-120nm, where covid-19 is 125nm so that sounds promising for mask use. this micron/um talk is confusing.
Hi Alan, the 1918 flu was 80-120nm which is 0.08-0.12um; so many viruses have a diameter about 0.1 um (100nm).
Filtration efficiency for the material making up the mask is great information to have, but it’s only part of the problem. For homemade masks, it’s practically impossible to get a good seal between the mask and the face, meaning that some aerosol is going to bypass the filter material and enter the respiratory tract directly. Have you considered doing fit factor testing to see if your choice of material actually makes a difference in the utility of these masks when somebody is wearing it?
Yes, fit tests are on our list of tests we hope to carry out! These machines aren’t expensive though, we currently have a campaign where we’re trying to raise money to buy a PortaCount, you can learn more here: https://fundly.com/best-diy-mask-materials
For better fit, try wearing a ring of nylon stocking over the mask: https://www.npr.org/sections/goatsandsoda/2020/04/22/840146830/adding-a-nylon-stocking-layer-could-boost-protection-from-cloth-masks-study-find
One idea is to use double-sided skin adhesive to create the seal. This was suggested by healthcare provider Unity Point Health –> https://threadsmonthly.com/free-fabric-face-mask-sewing-patterns/#unity-point
I doubt it will create an unbeatable seal, but it’s something.
Merv 13 filter , according to stats, filters 60% 0.3 to 1 micron .some has electrostatic charge too. Does not contain fiberglass. Mathematically calculated: 4 layers of merv 13 filter and plus inside and front of mask, is covered in addition with each layers of non woven anti dust mite 2 micron fabric, which is water repellent. So we have now 6 ply mask with still good breathability. according to mathematical calculation this mask should filter less than 0.3 micron particles with almost 99% any suggestions?
Can I put an ah10040 HEPA filter and a Scott blue shop towel in the fabric facemask?
Hi Ken, Liz here from Smart Air. Of course you can:) The breathability of the Scott blue towel fall on the good end, so it should still be easy for your to breath. We haven’t tested combined material yet, but adding an additional filter will definitely increase the filtration efficiency. The question is for how much. We have a plan to test more combinations and will publish the results when it’s available.
I did send a rather long comment which has not been posted. No problem. This does not need to be posted but I wanted Paddy and Thomas to know I think this social enterprise is great and I am doing what I can to spread the word!
https://www.thepmfajournal.com/blog/post/letter-from-hong-kong-8-may-2020
Hi Andrew, Liz here. Sorry about the late reply, and I already shared you article with the Smart Air team. Everyone’s very glad to hear your words and we are excited to see that readers like you are helping us to spread our researches and supporting our mission!
Have you tested a double layer of quilting fabric? An article in the April 5 2020 issue of the NY Times summarized test data for particles under 0.3 microns and various materials. They found that N,95 removed 95%, as they should, and surgical masks removed 60-87% while multilayer cotton bandannas removed only 18-20%, results pretty much in line with what you cite. However, they also cite results for a double layer of quilting fabric removing 70-79%, quite comparable to the surgical mask. Thus people interested in making their own masks might do well to consider using quilting fabric.
This is a great site and the info here is very timely. I am curious about incorporating HEPA filter media into a 3D printed facemask cartridge. Why didn’t you include the HEPA material in your recommendations? It seems like it performs really well and you can actually breathe through it. Also do you have any recommendations or guidelines for obtaining HEPA filter media? I’m looking at my vacuum bags, which claim to be HEPA.
Many thanks for your excellent work,
Richard
Awesome work! I wish you would specify brands and exact product names to make these tests more repeatable.
Material suggestions:
Bra cups may also be made of a cushy three-dimensional knit type called a spacer fabric; it has two surfaces and spacer yarns between them. It is also used for lining musical instrument cases, for car-interior covers, for hotel and hospital blankets (the thick, light ones, often also designed to absorb water), and sportswear. Some are very breathable (the stuff for shoes, for instance, is probably too open-pored). Most of it is synthetic, but some for bras and sportswear is cotton blend; not sure if the spacer yarns are ever cotton. Even if it does not filter well, it might be a nice inner layer for keeping your skin dry; sports spacer knits are designed for just that.
Hospitals would also appreciate a test of surgical sterilization wrap (https://gh.bmj.com/content/5/5/e002553 PMID 32371574), especially as a disposable-filter interlayer.
Would a bra pad and coffee filter be a good combination for a mask? Large supply of both in market. Just have to figure out how to put them together.
Hi Allan, We haven’t tested the combined materials yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
What kind of Hepa filter did you use?
Was it a vacuum bag or something different?
It seems Hepa was up there with N95, so the best material to include. I just dont know what to look for.
Hi Kate, Liz here. We used the H11 grade HEPA from our Sqair HEPA filter. We just torn the filter frame and flatten out the filter, cut a piece from it! I guess you can also try to source a single layer piece of HEPA filter too so you don’t have to deal with the glue! 🙂
I don’t understand. There is ONE material that clearly stands out on ALL the tests, yet you don’t mention it as a recommended material?! o_0
The materials you DO push did NOT do very well on the tests, or at least did not do well on some of them.
Why are you ignoring HEPA filters? In your own tests, HEPA filters came in:
– 3rd (99%) on the “1 micron” filtering; almost equal to the 3M N95 & the surgical mask
– 2nd (83%) on the “.3 micron” filtering; less than the 3M N95, but better than the surgical mask
– top-rated (++++++) on the “breathability” test; better than both the 3M 95 (+++) and the surgical mask (+++++)
Please explain this apparent oversight and give us more info on the specific HEPA filter you used in your tests.
Hi Tech! Song here. You’ve got a really good eye! The only reason we are being conservative on HEPA filter is we cannot be sure that whether the manufacturer making the HEPA filter making it safe enough as something to filter out breathing air so close to your nose and mouth.
This information is very helpful. Thank you! Have you tested cotton flannel?
I would love to see testing of combinations of materials in 2-3 layers to see how many layers would be the most effective while maintaining breathability. I love what you guys are doing!
This is something we’re working on in a follow up article. We’re working flat out to get this open-data out to the world!
Which brand of blue shop towels is the most effective. They are not made the same. Bb
The towel in our tests is Scott’s Blue Shop Towel. Hope that helps!
The math is this:
Let’s say something has an 83% chance of catching a particle. Then the particle has a 17% chance of getting through.
If you have n layers, the particle has to get “lucky” n times, so the odd of it getting through n layers is 0.17^n. The odds of a particle getting through 4 layers of 83% effective filter material is 0.17^4 = 0.17 * 0.17 * 0.17 * 0.17 = 0.000835 = 0.0835%.
https://www.khanacademy.org/math/ap-statistics/probability-ap/probability-multiplication-rule/v/compound-probability-of-independent-events
The problem may be trying to breath through 4 layers of something.
Hi Andrew, Liz here. Yeah, your math is right! However, in reality, the filtration rate is always affected by many factors. In a real environment test, we get the data and explain why is it different from statistic estimation. So the actual double layer of the same material’s filtration rate is lower than 1-0.17^2. Instead, it should be 1-[（1+n）-0.17]*0.83. n here is the dirty air that can come in between he two layers, thus the second layer is actually filtering out air already been filtered from the first layer + dirty air coming from outside. I hope this can answer at least part of the question:)
You are amazing by discovering new materials for facemask due to COVID-19 you are a hero
Thanks for what you are doing. Great info and I feel confident about it
This is great information to have. Thank you for making it available. I wish this would have included testing of a system laid our here [ https://enmed.tamu.edu/DIYmasks/ ] using polyester substrate in household heating, ventilation, and air-conditioning (HVAC) filters (MERV 13-16) sandwiched between two layers of polyester sheer fabric commonly found in sheer drapes or curtains. Two layers of MERV14 should be very close to N95.
Also, fit is very important, but perhaps that’s in another post.
Does a sheet from kitchen roll count as a paper towel?
Hi Debbie, Liz here from Smart Air. Yes, we used a sheet from our kitchen roll for the testing! Different brands may have different filtration rate, but you get the general idea!
Shout out from NYC. This article may save lives here. Thank you! Also, if you do further analysis, greater specificity about the materials used would be greatly appreciated.
Would you be willing to share the details of your equipment setup and process so others can test new materials and combinations? Would you accept data from outside testers for your database? I can’t afford to fund multiple materials, but I might be able to construct the test equipment here and contribute data. We could have several volunteers replicate the results for higher accuracy and validity.
Yes, please provide more detail on the methodology. Thank you!
I love this idea.
Since there was no reply to this question, I did a little more research. This video contains some good recommendations for testing masks: https://www.youtube.com/watch?v=8mCPB8n065Y
We can improve on the recommendations here as follows:
1 – Use corn starch as the particle source for the filtration test. Unlike flour (recommended in the video), corn starch has particles as small as 0.1 micron, in the range of the coronavirus. (Source: https://www.engineeringtoolbox.com/particle-sizes-d_934.html)
2 – Rather than relying only on visual inspection, make a starch detector with iodine. Spray dilute iodine solution on tissue paper and let it dry. Place over vacuum cleaner suction tube, solution side out, then place mask over the tissue. Rest the whole on a plate with corn starch. Operate the vacuum 10 seconds. Then, take out the tissue paper and mist it with water. If you see dark blue stains, some starch is getting through. This doesn’t give you a precise percentage, but you can compare different mask fabrics this way.
3 – To test for water droplet resistance, prepare a new tissue by spraying with dilute iodine, as above, and allow to dry thoroughly. Dust the tissue with dry corn starch. Place on the inside of the mask, between mask and the head of the vacuum cleaner. Operate vacuum cleaner, and mist plain water thoroughly in front of mask. (You don’t need to spray it directly on the mask.) Turn off vacuum, and remove tissue from within mask. If you see dark spots, water droplets are getting through the mask. Again, this doesn’t tell you a percentage, but you can compare different mask materials this way.
I plan to try my masks, an old N95 mask I found in the basement, and a few different components (bed sheet cloth with different counts, etc.) and I’ll publish my results.
Amazing post! It is important to use masks to prevent transmission of virus. Medical stores are running of out stock. Preparing our own masks is a better option. We can reuse them after washing properly. Thankyou for sharing the information.
Very helpful information – thank you for your report.
Any good testing should include backpressure or resistance to air flow. If you can’t easily breathe through it then people won’t use it. Pressure drop across the filter media causes air to leak sideways instead of through the filter. Backpressure is easy to measure with a water filled tube manometer.
People really need to know how quilting cotton and various interfacings fare in the test, since millions of masks from these materials have been donated and sold, and so many patterns call for them.
Can I use garden lightweight Frost cloth as a mask filter
Best Reusable and washable facemasks!
Hi! what about TNT fabric? it is good for diy mask?
thank’s
Great review! Just wanted to let you know that Scott’s shop towels You tested aren’t the ones that were supposed to extremely work well. The shop towels tested were hydro knit (wypall, toolbox) whereas Scott’s towels are just cellulose.
It’s really a useful blog.
visit Meddco Healthcare: https://www.meddco.com/ for affordable healthcare packages
Thank you keep sharing.
I heard from another site that cotton quilting fabric is good. I made a mask with a pocket out of a similar fabric. Would using a kitchen paper towel be good as a filter? It seems like it would, according to the chart above.
Hi 120 threads bedsheets are very difficult to find (I am still looking for one!) 250 threads is more common. What was your result with 250 threads? And does it have to be 100% cotton? Thanks!
Yes, I agree. Are higher thread counts just less breathable, or are they less filtering? I would think they would filter more. Please let us know!
I noticed you mentioned Hero and Chemex coffee filters. I’m familiar with the Chemex brand but I can’t find a Hero brand. Were you referring to the Hario brand, not Hero?
Hi Mario, Liz here. HERO is a Chinese coffee equipment company. The filter is an original paper color (not the bleached white one) V60 filter. I think you can find something similar in your local store.
Thanks for the reply with the model number. I believe you’re referring to HARIO. When I Google “V60,” I’m getting HARIO results. Also, they’re from Japan, not from China.
: )
is the effectiveness additive if I use more than one material
Hi Phil, we haven’t tested multiple materials yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
@Phil, apparently yes, well not really additive but at least improved : “One layer of a tightly woven cotton sheet combined with two layers of polyester-spandex chiffon—a sheer fabric often used in evening gowns—filtered out the most aerosol particles (80-99%, depending on particle size), with performance close to that of an N95 mask material. Substituting the chiffon with natural silk or flannel, or simply using a cotton quilt with cotton-polyester batting, produced similar results”. cf https://phys.org/news/2020-04-material-homemade-masks-combination-fabrics.html
Also “cutouts of nylon pantyhose over the masks improved the effectiveness of all masks”: “the nylon layer, which presses the masks closer to the face and keeps the air from circuiting around the filters” https://medicalxpress.com/news/2020-04-pantyhose-toilet-paper-coffee-filters.html
@Liz, that would be great if you could replicate both of these studies.
Hello,
How about disposable c-pap machine filters? They hit the .3 micron mark at least apparently. A healthy non-toxic /less toxic fabric to breath is key too & unsure how these fair.
Also, most all homemade masks don’t have a pinched nose area & it’s evident (by self study) that it’s a significant point of air flow; perhaps more important in a healthcare or large social setting (someday).
Thank you so so much for your quick, informative, & nicely laid out research data on this vital mask issue. You rock, as do the financial supporters of your work!
Can you test silk please and if you do, specify what thread count you are using?
I found this study (24 April 2020) that included silk –> https://pubs.acs.org/doi/10.1021/acsnano.0c03252?fig=fig3&ref=pdf
Why don’t you test the material used in furnace filters? Filtrete’s Elite Allergen claims to filter out .03 microns. I’ve been making filter inserts for cotton masks from 400 thread count sheets. I wish I could get them tested.
Hi Linda, Liz here. We’ve been getting many request on testing furnace filter. We haven’t tested it because there’s a concern of whether the material is safe to be made into a mask that may have direct contact with our skin and whether it is designed for filtration breathing air. We are working on more tests and will share the results in the blog!
Please test different HEPA vacuum cleaner bags, Hoover, Miele etc.
I posted a question but don’t see it so assume it fell through the cracks. There are 2 man- layer masks described on the internet, one demonstrated by the Surgeon General of the US, that I hope you will test.
1. The one demonstrated by Surgeon General can be made from a bandana or handkerchief and has 8 layers
2. The other, the one I made from a handkerchief, is folded so that it has 6 layers.
Both are attached to your ears with rubber bands
I hope they can be tested.
What about micro fiber towels?
Hi Gilbert, we haven’t tested micro fiber towels yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
Army tests indicate microfiber cloth masks are very effective. See https://www.armytimes.com/news/your-army/2020/04/24/army-researchers-say-this-is-the-best-material-for-a-homemade-face-mask-theyve-found-so-far/
Hi Paddy,
I would like your permission to include some of the scientific information you provide in your blog in emails going out to our customers and subscribers in the UK. This is because there is plenty of false information on social media and I think people would appreciate some clarity.
Thank you.
Best regards,
Bob
Hi, Bob,
Liz here from Smart Air.
Our policy is that anybody can use and recopy our open-data, if they include a reference. If you’ve done this, then we have no issue. In fact, it’s great to see people like yourself further sharing our open-data! We need more people like you sharing fact-checked, informative info to counter all the misinformation that’s online right now.
Hi I read the article with the various types of materials tested and saw the natural fibres samples did not fair well -the scarfs. The problem i have here is that we not comparing apples with apples. The weave structire of the scarfes vs the other are not the same. If the woven structure is the same, including yarn thicknesses etc, a better comparison will be observed. As the article explained natural fibres should have proved to be better, because of the unevenness of the fibres etc. Wool for example is known to be a very unique fibre naturally compared to man made fibres. Also looking at the different fabrics used one also compared different structures – woven, non.woven and knitted samples with one another and each sample thus will give different results- again not comparing apples with apples. But yes one should start somewhere and test DIY fabrics currently on the market and from this I find the results very interesting. Glad to see the double layer t-shirt material performed well – natural fibre cotten – a very good absorband material like wool. I still say try a similar structure with wool – you might be supprized
Thank you very much Liz.
Is that policy an official license, CC BY-SA or some such? If so, it could go on Wikipedia.
I work for a company that makes non-woven materials. Is it possible to submit a few for testing?
Hi Stephanie, I just shoot you an email on testing process and cost details.
Confused about the effectiveness of paper towels. This article states it’s one of the best materials, but your other article “DIY Masks: Is Paper Towel Effective at Stopping Viruses” says of paper towels “the results weren’t great” and goes on to conclude that they are “better than nothing” – not much of a recommendation. The two articles literally give different statistics on the effectiveness of paper towels for .3 micron particles. Given that this is one of the most common materials that people have around their house, can you clarify this disconnect? (By paper towels I’m referring to kitchen-style paper towels, not the “hand-drying” type).
Hi Kevin, as you may see the paper towel filtration rate for 0.3 micron particles is 33%. That is not a good number compared to the N95 masks. I personally won’t wear that if I’m going to a hospital or any place with high infection risk. However, the breathability of it is fair. I may use it as a DIY mask material if I’d wear the mask in my office of when I do exercise outdoors. the first article emphasize more on the material’s filtration performance alone and the latter article is our comprehensive understanding of the DIY mask materials. Hope this answers your question.
I am curious to know how these materials work when wet. Even when soaking wet. I imagine it can be very hot in the summer, it would be nice to make your (e.g. cotton) mask wet to cool down.
What I keep looking for is information on Non Woven Interface – Pellon has many kinds, thickness, fusible, etc. I have read 2 pieces of 100% cotton due to this being a tighter weave. No center seams. 2 pieces of non woven interface – I read some place and I believe your article stated the poor mans test – can I see through it. I’ve made with Pellon 809 ( all I could get my hands on ), very stiff interface, made basic mask with pleats. Couldn’t find metal. Used shoe strings for ties. About 95% of people are okay wearing and breathing through it. I have extremely sensitive skin and makes my cheeks hurt. I used a Pellon 830 non woven interface ( very thin, for pattern tracing ), I can wear this longer but still irritates me. I’ve tried asking Pellon about if this material is safe to breathe through – no response. How do we know if the material we are breathing through is even safe?
Hi Janet, you won’t know unless you can get the detailed info from the manufacturer. Polyester and viscose, which is listed on the Pellon 830 should not be harmful. My concerns is the manufacturing process may left harmful chemicals on the material, or tiny fibers may shed while you breath through it.
Liz I have read things like that with clothes in general; harmful chemicals that are on our skin and that we inhale. Do you know if the chemicals wash out; are they always shedding the life of the fabric, in general? Is cotton safe to breathe in if this is the outside case of the mask ( again the material is intact, no center seams )? Pellon won’t respond to me 🙁 not a lack of trying
I thought about interface, too. But I’m not sure it would work better in practice than two layers of quilting fabric, etc. My reasoning is: natural fibers work better at blocking microscopic particles than synthetic fibers, in general. The melt-blown non-woven synthetic fabric works very well to block microscopic fibers, but spun-bond fabric can’t be substituted, even though the equipment to make it is more common, because the fibers are larger. I think it is highly likely that interface fabric is spun-bond. I would definitely not recommend fusible interface because the adhesives used may affect breathability and have not been tested for toxicity in this application.
E. Dalton – your comment about interface. Trying to make sure I’m following you. The interface that I have is Non-woven ( you can purchase woven or non woven). If I hold it up to a light you can see the structure is different. Now I understand that non-woven material can be manufactured differently and their are different standards. Surgical masks I know are made up of non woven fabric created using a melt blowing process, I have seen 3 ply 25GSM, which takes me to polypropelene ( i think ) non woven fabric ( again, I do not understand standards and cannot get anyone who deals with it to respond ). I understand the masks are more for catching droplets inside and outside of it. So back to DIY – if I have 100% cotton on the outside and cased inside is non woven interface. Cut on a fold and cut into a square, so trying to keep the material structure intact. Do you still believe we are breathing microscopic fibers? I have Pellon 830 – 70% polyester 30% viscose, 931TD 100% polyester, 915 100% polypropene, 809 100% polyester ( it states the glue washes out – not sure that is 100% true or not ), 380 100% nylon and 910 85% polyester and 15% viscose. Again all non woven. Still concerned about lungs. And concerned about vacuum cleaner bags, blue paper towel, coffee filters etc – if someone cuts this, you let loose fibers? Should you even be breathing through things like this.
I don’t think any of the interfacing has fine enough fibers to be better than quilting cotton. The “non-woven” fabric used in medical masks is made with different equipment that produces micro-fibers. Sewing interfacing is made with larger fibers that are spun into threads first, then melted together to make stiff fabric. Multiple layers of quilting cotton or high thread-count sheets will probably work best. If you are using a non-cotton layer, put a cotton layer between the non-cotton layer and the face for safety. Remember, 100% natural fibers will be better tolerated by the lungs if a few stray fibers come off during use. The body can break down small amounts of plant fiber. (We breathe in some plant matter normally, e.g. pollen.) Plastic/synthetic fibers build up in the lungs. Hopefully a cotton layer would block stray synthetic fibers. Washing thoroughly before use will possibly help, but I would avoid synthetics entirely. I have seen guidance from either the WHO or the US CDC saying to avoid adhesives of any kind, so I would not use any fusible products. Even if they are not toxic, they would reduce breathability.
Obviously, actually testing these fabrics would be more accurate, but just from a materials safety point of view, this is my best recommendation. I hope this helps.
Very helpful. I would like to see testing done on more than one or two layers. I am using a mask made from a handkerchief and rubber bands for the ears that has 6 layers. On the internet, the Surgeon General of the US is demonstrating how to make a mask that is folded different from mine and ends up with 8 layers. You say one additional layer doesn’t add much but what about 5 or 6 additional layers?
Hi Ken, we haven’t tested multiple layer materials yet. We know there’s a huge demand for reliable, science-backed data right now, so we’ve created a campaign to gather information on what our readers want to test. To vote on what test you expect to see and support our campaign, visit our Fundly.com page here: https://fundly.com/best-diy-mask-materials
Thank you so much! I am curious what kind of HEPA filter was used? Was it a fabric like vacuum bag, paper vacuum bag, or from an air filter? If possible, also brand and type?
To me the HEPA filter was the absolute winner! Best filtration and best breathability. I don’t get why it’s not in the top 5 tbh.
Why was HEPA filter not recommended when it’s breathability was 6 and filtration of smaller particles 99%? I have HEPA fabric cut out from a furnace filter with high MERV that I was thinking of slipping in between layers of quilting fabric. Also, what MERV rating was the HEPA you tested?
Hi Melanie. Song here. Yes, HEPA filter performs well. The only reason we are being conservative on HEPA filter is we cannot be sure that whether the manufacturer making the HEPA filter making it safe enough as something to filter out breathing air so close to your nose and mouth.
I have been making the N95 mask cover extenders (fabric ties) with bed sheets that are 300 thread count. I hope this thread count is good & considered breathable. For some masks for non professionals I added wire to stop air leaks at the top & so glasses wouldn’t fog up. This is needed because non professionals use this mask without the N95 underneath. Also please let me also know if there is a preference in styles of mask coverings for breathability between the N95 style and the pleated style with elastic.
Hi Paddy,
Thanks for performing these analyses! We’re all kind of flying blind when it comes to our DIY masks, so any kind of quantitative testing is a welcome change.
There seems to be ongoing confusion over what particular shop towels people are using. The Business Insider article that may have helped first popularized the idea of using shop towels (https://www.businessinsider.com/homemade-mask-using-hydro-knit-shop-towel-filters-better-2020-4) mentions a few brands, but it’s not obvious exactly what products they used.
Here’s a link to the website for Sellars brand wipers, which includes a nice table summarizing their product lines (https://sellarscompany.com/wipers-tools/selection-guide). I’m not sure, but just based on appearance the “Toolbox Shop Towel” mentioned in the Business Insider article might be the Z400 product.
If you have the time and resources, it would be interesting to run your test on several of the different shop towel products and see if there’s some correlation with any of the properties on the table (e.g. “wet strength”). In particular, I’ve been making masks out of the Z900 shop towel and the X70 and X80 shop towels from Wypall (similar to Sellars T700/800), so if you repeated the analysis on those, I’d be especially interested!
Best,
Chris
Thank you Smartairfilters team for conducting the tests and generously making it publicly available for DIYers.
Found this layer combination by a Singapore research institute that they tested with results pretty close to surgical masks.
Would be awesome if your next round of test could consider this layer combination.
https://www.a-star.edu.sg/docs/librariesprovider1/default-document-library/news-events/news—content-block/astar-diy-mask-science_website_apr-2020.pdf?sfvrsn=90a9312c_4
Could you please test Pellon brand, 809 fusible interfacing for use as a filter. It is 100% non woven polyester with a fusible backing. I use it single layer between 2 pieces of 100% cotton fabric. If making masks for healthcare, I use a double layer of the interfacing. I have two styles of masks that I am making; they typical folded mask, similar to the surgical mask and one that I patterned after an n95 style mask. The n95 mask style fits tigher around the cheeks, nose and chin and because it is not directly against the nose and mouth, it is easier to breath through the 4 layers (2 interfacing, 2 cotton)
Thank you in advance and I hope to hear from you soon.
Love this article. For paper towels is it taking your standard store bought brawny type paper towels?
Hi Amanda, Liz here. We just used a Chinese brand called “心相印” which is available in most grocery stores. So it should be similar to the standard paper towel you can get in your local store!
Hello. I I love all your articles regarding your testing on various household materials for masks.
Is there any way you can test the efficacy of a fabric mask made with 100% cotton, two layers, and sandwiched in between is one layer of pellon 915. Using the surgical style mask pattern with 3 pleats.
Thank you a bunch!
Sunny – my question is, is it safe to have Pellon 915 in a mask as you stated; surgical style, pleats, assuming cut on fold, stitched 3 sides. Pellon 915 is 100% polypropelene inside and 100% cotton outside. Is it safe to be breathing through this? Is it safe to be breathing through 100% cotton even? Most everything has microscopic shedding? Maybe I am the anomaly 🙂 I think most everyone is worried about the virus and I’m worried about our lungs.
Thank you for the work you’ve been doing. The information you have shared is very helpful.
I noticed that you tested cotton sheets with low thread counts. Could you test cotton sheets with a range of higher thread counts (e.g., 200, 400, 600, 800) to see whether a higher thread count does better job of filtering small particles, and also compare the results for a single layer vs double layer?
Intuitively, it seems a higher thread count would be better (though there might be a tradeoff on breathability). Still, I’d rather know before I start turning my one set of high-thread-count sheets into masks.
Thanks!
Why not test gore-tex?
You link to a disturbing picture with animal testing. There are better ways to explain what a Henderson Apparatus is. https://www.tradelineinc.com/reports/2007-5/hpas-precision-aerosol-exposure-and-containment-technology
Thank you for your work. This is very useful information. What specific type of Scott’s shop towels did you use in your experiments? (original or heavy duty or ?) Thanks.
Hi Dawn, we used the most common original one.
Thanks for all your detailed work.
As I was reading your article, which is extremely informative, I was making notes of materials that could be used for masks. I didn’t see Spandex, felt, polyester (slacks) and tube socks for starters. My mind is reeling as I write this message. But, I will be checking back to see any updates you may discover. Thank you for your diligence in this project. I means a bunch to me and my family, and to thousands of others, too. I will be posting this on my Facebook page.
The study says one and two layers were used. It’s important to know when you used one and when you used two. Also, does “coffee filter” refer to the WHOLE coffee filter? If that is the case, that makes it technically TWO layers, right? So did you use one whole filter (two layers) or two whole filters (4 layers) in your study?
Forgot to throw a “thank you” in there lol sorry. This is a useful study.
Thank you!!
Hi A, Liz here. All of our tests so far are done with one single material one single layer. So for the coffee filter, we cut it into one layer sheet and tested it.
You should put a note that your “kitchen towel” is paper. I didn’t even know there were two types of paper towel; I would assume “kitchen towel” was cotton. I hope you test cotton towels in your next round, both smooth and terry.
Adding to my previous post (if it passes moderation), I just tried placing a stainless steel un-soaped pan scourer between my mouth and my mask (suitably shaped to extend over the complete mouth area). A little uncomfortable (but not horribly so), but what a difference in breathability and moisture build up! Maybe not the best solution, but it does prove the concept.
PS – Happy to have this edited and added to my previous post. 🙂
It’s also worth considering an internal structure to stiffen and expand the area in front of the mouth through which air is inhaled. If the filter is collapsing onto the mouth, then the airflow is concentrated in a very small area right in front of your lips, which will be one of the reasons why breathability is low for some of these tests.
Making sure the filter is kept away from the mouth means air has a much larger surface to pass through. This larger area will also help with preventing moisture concentration from the outbreath, which also reduces breathability. Have a look at commercial masks; they have ribbing pressed into the filter material to stop them collapsing.
I’m about to explore what would make a good front of mouth structure for my ‘home made’ cloth mask. Mini sieve – tea strainer? Copper wire soldered into a shallow dome (wrap it in tape or you’ll get green marks where it rubs against your skin). A 3D printed structure? (Maybe that already exists?) There’s bound to be something out there that’s designed for another use but will make an ideal support structure.
My mask also has a pocket to hold HEPA filter material – chopped up HEPA vacuum cleaner bags!
What about one way nappy/diper liners for filters
I haven’t seen a lot of data on the relationship between dry particle filtration and the probability of catching an infection. If I understand correctly, the covid virus is usually traveling in a water droplet, which presumably is quite large. I would think that other characteristics like the ability to absorb moisture, being hydrophilic (or not), might actually be more important that pore size.
Amazing work, thank you for what you do.
I work with recycled cotton (mainly denim) and polyester making airlaid felt (randomized fibers are bonded with resins and made sheets).
Final product are thick (5 mm and upwards) sheets that can be bent, cut, sewn, etc.
I think the randomized material would be good at catching particles (not that great for breathability).
I’ve seen filters for machinery made from airlaid polyester felt, but can’t find anything on face masks.
Do you have any information on cotton / polyester felt for masks?
The 1.0 and 0.3 micron graphics have disappeared from this article… maybe they got moved?
What is “canvas” exactly? Is that like normal sewing fabric, the material most people are using for their mask?
Hi Alex, it’s 100% cotton, like the canvas you do oil painting on. The thick ones are used in painting, and the thin ones can be found in making some DIY eco-friendly bags.
Hi Alex, it’s 100% cotton, like the canvas you do oil painting on. The thick ones are used for painting, and the thin ones can be found in making some DIY eco-friendly bags.
This is all wonderful work and thank you! However, you’ve yet to incorporate this very relevant research published in Nature 2017: https://www.nature.com/articles/srep39956 It clearly shows that salt impregnated paper not only filters but also denatures similar virus under laboratory conditions, thus rendering the home-made cloth mask with this filter superior to the surgical mask for protection from COVID. PLEASE READ and TEST Also I think you should point out that the N95 mask only filters the inhale – the exhale valve bypasses the filtration, as such it is a totally selfish thing to wear in a public situation and only suited to medical environment where it is worn by regularly tested medics. In our publicity we say you can actually hear the “me me me me” sound of the exhaler flap if you listen closely 😉 I would love it if you would run your particle test on my home made salt impregnated paper filter inside double layer of t-shirt. We are currently making and distributing these in Bali which does have an astonishingly low rate of transmission. Here’s my tutorial : https://www.youtube.com/watch?v=Rsw0yqBWsAM Wouldn’t it be amazing if the solution was really this simple!!! The published research certainly suggests it could be! Well done Smart Air
What type and brand of “paper towel for hand drying” did you test?
Hi Wander it’s Kleenex Premium Folded Towels.
Why wasn’t HEPA filter in the top five? It scored high in particle filtration & breathability.
Hi Cassandra, we have two concerns: we are not sure how safe it is to make a DIY mask having directly contact with your mouth and skin using HEPA filter and the HEPA material is not soft so the fitness to our face would be worse than other materials. So we didn’t recommend to use HEPA filter making your DIY mask.
So might it be OK as a replaceable middle layer between two cotton ones? Or as refills for gasmask-style filters? There are a lot of cotton masks with a pocket for an insert, it would be great to have some insert testing (maybe once you get that PortaCount Pro+ Fit Test machine!).
I want to give to your fundraising on https://fundly.com/best-diy-mask-materials but you loose 8% and we can only pay in USD (which adds conversion fees). You should set up a paypal account or something else.
Thanks, Pony! With PayPal we would also lose 5% on fees, but yes – it’s less than the 8% on Fundly. Neither are ideal. If you do want to donate via PayPal, you can do so using the link: http://paypal.me/smartairfilters (Please make sure to use note FUNDLY MASK DONATION)
Thanks Paddy, should I send you the money via paypal in USD or in another currency (as the paypal account seems to be Chinese)? My currency is euro so in any case there will be a conversion, but it’s better to avoid making multiple conversion on your end.
I just tried with paypal, but the fee is even higher as this is a donation and not a purchase. I give up, it would be nice, if you have a euro account.
Yes, just create a giro account in Europe, give the SWIFT/IBAN info they tell you on your website, and anyone in Europe can do a giro transfer to you. Much cheaper.
Agreed!
What brand paper towels were used?
Please try combining 100% cotton fabric with a non woven fabric such as Pellon for sewing
Can you try 100% cotton combined with a non woven fabric like pellon?
Great work! Based on your preliminary results, I’ve been making masks with 3 layers: 1) inner lining of heavyweight cotton jersey knit, 2) filter layer of cotton tea towel, 3) outer layer of fine woven quilting cotton (probably similar in characteristics to the bed sheets you tested). I prewash all fabrics in hot water before assembly. The resulting masks are fairly breathable, but I wonder if the combination works better than only the single most effective component? I think brownian motion might be increased by the different types of layers, but without an empirical test, I can’t be sure. Would you have time to test some combinations of your existing materials and report the results? I know previous tests have included doubling the same component, but I’m interested in knowing if different layers might take advantage of the properties of different materials. If nothing else, the jersey layer seems the most comfortable against the face, and the tea towels have more of a tendency to snag and pick up lint than the quilting cotton, so the three-layer combination might have practical value, even if it isn’t much more effective at blocking particles than the kitchen towel alone. But if a combination of heavyweight jersey and high percale sheets works just as well, they would be easier to assemble.
what about masks sold on esty that have an opening and holder for a hepa filter?
Fantastic work. Thank you very much. I think the next logical step would be to:
1. Try different cotton t-shirts to see if there is a way to reproduce the Cambridge results.
2. Try different brands of paper towels.
3. Try different configurations of paper towels, such as 1 layer, versus 2 layer, versus 3 layer, as well as moistened versus dry.
4. Try two or even three different materials in series. I bet some unexpected results would happen here.
Thank you for the testing. A few questions. You rank “paper towels for hand drying” highly. But in previous tests paper towels rated poorly. Are these different paper towel types or has something changed in your testing methodology? Not all materials are listed under the breathability rating – I don’t see shop towels there.
We tested two types of paper towel, a kitchen towel, and a paper towel for hand drying. We found the kitchen towel was not especially breathable, which is why we didn’t recommend it. The type of paper towel you use will definitely have an impact on its particle capture effectiveness. Thin paper materials like toilet or tissue paper are unlikely to have high particle capture rates!
P.S. we’ve updated the table with shop towels – good spot, Bill!
When you say paper towels for hand drying,are you referring to the ones found in retail store public restroom that come on a road? Or restroom paper towels that are in a dispense one at a time dispenser?
Hi Marilyn, we used the Kleenex Premium Folded Towel.
What is a paper towel for hand drying? Is it more like a sho towel? Did you have a brand for example?
Photos of the “paper towel for hand drying” would help me a lot. I can think of a couple of different paper products that I’ve seen used for that, and I wish I knew what kind you tested.
Thanks Paddy. I’m based in the US and what we commonly refer to as paper towels are what I am guessing you mean by kitchen towels. They were the type shown in your first video. Example https://bountytowels.com/en-us/shop-products/bounty-paper-towels. I’m not sure what type of towel you mean when you say “paper towel for hand drying”. There are a few varieties found in public restrooms. Such as the various varieties sold here: https://www.newegg.com/georgia-pacific-cleaning-wipes/p/N82E16848043079?nm_mc=knc-msnsearch&cm_mmc=knc-msnsearch-pc-_-pla-_-os+breakroom+cleaning-_-georgia+pacific-_-48043079&msclkid=c8ec9c4d52e91bc465e8c2ed95d01eaf&gclid=CNKD7NWM_egCFaOrxQIdticAVg&gclsrc=ds
There is also a type that is about 4x thicker and found in high end restaurants. So not sure which of these are the “paper towel for hand drying”. Would be helpful to verify which type were in your test.
I was given a DIY Tool Box shop towel,Staples,Scotch tape,rubber band mask. . The fit is very good,hugging the face and under the chin. Breathability was not good at all. The towel,as near as I could tell,had been folded over the long way to where it was doubled? It is not easy to breathe w it on. I hhad to keep sliding down to catch a good breath
By “paper towels for hand drying” do you mean the (usually brown) folded paper towels often found in public restrooms?
Thank you for yet another tremdenous resource for we makers of homemade masks!! I am wishing/suggesting that you add info/clarification on those materials that are strictly used as inserted filters in a mask as opposed to used for making the entire mask. While all can figure out that one cannot make an entire mask out of a coffee filter, some, eg, may not be so clear about HEPA filter material. What are results if use 100% cotton t-shirt material (or bed sheet, or whatever) for the mask and then add a HEPA filter insert? Also, in my community, using Filtrete furnace 1900 or 2200 filters is popular as a mask insert. Is this material like what you used in your study? A little info on just what your study used for when you state “HEPA filter” would be helpful. Also, vaccuum cleaner HEPA filters have been suggested/recommeded at some home sites. Is this a good idea – or may they have particulates that would not be good to inhale??
I be read Hepa filters contain harmful materials.
This is my question as well. What HEPA filter was used specifically?
Thank you for doing this extensive study—it’s much appreciated!
Hi Martin, Liz here. We used our own HEPA filter for our DIY air purifier: https://smartairfilters.com/cn/en/product/hepa-filter/
I’ve read quilting cotton makes good masks. It is a tight weave 100% cotton that comes in beautiful colors and patterns. Did you test any of this material yet?
Yes! Quilting fabric – 100% cotton is a highly used material in the mask making world. Typically 2-3 layers is common as 4 layers become hard to breath through. Can you please test 2-3 layers of 100% cotton quilting fabric and give us your input? Thanks for this!
Quilting cotton should have characteristics similar to the 100% cotton bed sheets that were tested. Since quilting cotton also varies by brand In thread count, thread size, and tightness of weave, it would be hard to provide any more reliable data than that. It’s critical to wash the fabric in hot water to pre-shrink and remove any sizing, excess dye, etc.
Just as a complement, knitted fabrics (generally) are more elastic than woven fabrics. When you put a mask on your face you stretch it so that it fits well. If the fabric is elastic, the pores will tend to open and this will increase the possibility of particles entering in it. Fabrics such as T-shirts or those that contain Lycra, for example, can generate this effect.
Congratulations for the excellent and helpful work.
This is an unusual intersection of engineering/physics and sewing. I’ve tried to make both ends comprehensible, trusting that people from both ends will excuse me explaining the obvious, and correct any errors (learning skills across boundaries of cultural and gender occupational segregation can be a seriously useful advantage:defy socialization! Take up a hobby that clashes violently your self-image today!).
Stretch can be quantified: if you pull with force X, and it stretches by Y, then X/Y is the Young’s modulus. This measurement requires, minimally, a ruler and either a forcemeter, which is quite cheap, or hanging weights. If you measure the stretch (strain) at all achievable force (stress) levels, you have a stress-strain curve. The shape of the stress-strain curve tells you a lot about the material.
Woven cloth is usually anisotropic, with the highest Young’s modulus on the bias (diagonal to the threads). The warp grain (along the threads that run through the loom, along the length of the bolt of cloth) is also often substantially less stretchy than the weft grain (the threads that go back and forth across the loom; the warp, as the name suggests, may be under more tension during manufacture). Knit cloth may be pretty much isotropic or dramatically anisotropic; plain knits, the sort you might make yourself on a set of knitting needles, are fairly isotropic, but some machine knit patterns are dramatically anisotropic. Non-woven fabrics (paperlike) are usually isotropic. Returning to the forcemeter, you can pick a realistic force level, and plot the amount of stretch in a given direction in a “polar plot” drawn on the fabric. Or skip the forcemeter and just try for a consistent pull with your fingers. This gives you a strain figure which is probably a symmetric or semi-symmetric four-point “X”-like star; the points are the directions with the most stretch, with their length proportional to the amount of stretch. You can probably imagine this shape in your head, but chalking on the fabric works.
Cotton canvas becomes dramatically tighter and stiffer when wet (which is why canvas buckets work). My experience is that cavasses vary widely in stretchyness, with lighter cavasses, with a more open weave, usually being stretchier. The type of cotton also seems to have an effect.
When you stretch textiles, especially anisotropically (not evenly from all directions: for instance when a heavy piece for fabric is hanging vertically, with its own weight pulling it into a taller, narrower shape), then, as Luís said, the visible holes can change dramatically (think fishnet stockings, or a fabric with staggered parallel slits in it). Choosing stretchier fabrics has been advocated to improve mask fit. I’d be fascinated if you picked a material showing dramatic stretch-dependent visible-hole changes, and tested it stretched anisotropically in various directions. I’d also be fascinated by a study comparing straight and bias-cut masks of the same materials, if you have anyone local who could run up some of each.
Inexperienced sewers sometimes cut and stitch dramatic tensions into their cloth, leaving some of it permanently stretched. Any good sewing-machine manual has instructions for troubleshooting sewing-machine-settings causes for this, and testing on a scrap until your seams are smooth. For cloth that does not slide easily without stretching, sandwiching it in tissue paper and stitching straight through can help. The easiest seam is a straight line along the least-stretchy grain, on both sides. Problems can be caused if the grain orientation is not as symmetrical as possible across the seam, bearing in mind that mirroring the warp with the weft may not work if one is much stretchier (that is, the strain circle plot should be mirrored across the mirror-line of the seam). This might also come into play in a good mask design. https://www.makemasks2020.org/ has a pattern library, and has gone with a straight-cut pattern.
And how would that change if it was two layers? Thanks
We hope that our next round of tests can look at how multiple layers affects each material’s performance. If you’d like to see this open-data, then please support our fundraiser to make this possible!
https://fundly.com/best-diy-mask-materials
Hello, thank you for the tests. Did you try your best combination, for example a sandwich of bed sheet / paper towel / bed sheet as a single unit?
We hoping to get round to multi-layer and sandwich layer tests in our next round! We’re working as hard as we can on this research, but if you’d like to see this open-data, then please support our fundraiser to make this possible!
https://fundly.com/best-diy-mask-materials
I have looked everywhere and cannot find Hero brand coffee filters. Where do you buy them??
Hi Beckie, HERO is a Chinese coffee equipment brand. the test used the original paper color (not bleached) V60 filter. I think you can get a similar one from your local coffee shop. The issue is coffee filter’s breathability is not very good.
Interesting work! Congrats!
However, fabrics should be described using textile parameters from textile engineering: fabric type and fabric structure (plain, knitted, round-knitted, double side knitted, nonfabric, etc or using the typical names like jersey, double-jersey, rip, Lacoste, woven plain, twill, etc., fabric density, fabric thickness, cover factor, filament type (monofilament, multifilament), fibres type (fibres nature, mean fibres length), fibres title (thickness and or density) fabric nature (cotton, wool, linen, viscose, or polyester, polycotton, polyamide, etc). Otherwise, it is not easy to understand and to use the results in the practice. It would be interesting to classify the samples from a technical standpoint. You should be assisted by a textile engineer.
Regards,
Agreed that characterization of fabrics is a weak point in most of these studies; I’m very glad to see you giving threadcounts and distinguishing scarf and T-shirt fabrics. I’ve seen canvas sold by weight per unit area, especially in marine use; I don’t know how well that correlates with thickness.
Yarns with low volume densities/dernier weights (“den”) are fluffier and might thus make better mask materials. https://en.wikipedia.org/wiki/Units_of_textile_measurement has more relevant terminology, some cotton-specific. If you put out a call for common fabrics with certain traits, expressed in terms the textile industry can understand, you might get mailed an expert selection of promising samples. If you could correlate industry terminology with utility in masks, even quite loosely, that would be wonderful. It would be nice to be able to buy fabrics with some estimate of likely mask usefulness.
A guide on how to determine thread count on a fabric: http://vettycreations.com.au/white-threads/2010/10/12/tutorial-how-to-determine-thread-count/
There is a lot of terminology associated just with bedsheets, and apparently some legal ways of inflating threadcount by counting multiply threads as multiple threads:
https://sewguide.com/thread-count/
https://www.thespruce.com/bed-sheet-terms-thread-count-weave-and-fabric-350479
Higher threadcounts are more expensive. If higher threadcounts are more protective, and academics have more expensive bedsheets, they could wind up recommending “bedsheets” or “pillowcases” to poorer people who then make something which gives them much less protection than the academics measured.
I am an amateur, and maybe there is something I am missing here, if so please clear up my confusion….
You stated:
“The Covid-19 coronavirus measures 0.06-0.14 microns in size, but 5-10 microns when in droplets.”
Your tests include data on 0.3 and 1.0 micron particles.
The CDC says:
“The virus that causes COVID-19 is thought to spread mainly from person to person, mainly through respiratory droplets produced when an infected person coughs or sneezes.”
https://www.cdc.gov/coronavirus/2019-ncov/faq.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fcoronavirus%2F2019-ncov%2Fprepare%2Ffaq.html#How-COVID-19-Spreads
Whether this coronavirus is likely to spread through airborne means – the smaller particles – is still under study:
https://www.npr.org/sections/goatsandsoda/2020/04/03/825639323/scientists-probe-how-coronavirus-might-travel-through-the-air
The way I read it, the consensus now is as stated by the CDC above, it’s mainly through droplets.
So, why not do your tests on 5-10 micron sizes, and focus your conclusions on that?
Quoting your results for 0.3 microns is misleading – given present understanding, particles that small are not a primary means of transmission. Even 1.0 microns is small, and given the big differences you found between 0.3 and 1.0 microns, there might also be a big difference between 1.0 and 5.0.
At the very least, suggest your article include an explanation of this.
Very good point, Tom! 0.3 microns is typically referred to as the ‘most penetrating particle size’, or the most difficult particle size to capture. We used this in our tests to give the most conservative numbers possible. All the materials will likely do much better at capturing 5-10 micron particles!
You can read more about why 0.3 microns is so hard to capture in this article: https://smartairfilters.com/en/blog/what-is-pm0-3-why-important/
It is my understanding that as the larger sized water droplets that have carried the virus to the surface of the face mask evaporate from the mask, the particles that were in those water droplets are left behind on the mask. So the 0.3 micron coronavirus is left behind on the mask. It can travel through the spaces in the mask material when the person wearing the mask inhales. It is important then to wear a mask that can block 0.3 micron particles. It is also important to properly handle a contaminated mask to avoid infection through touch.
I think because if it can catch the larger it can catch the smaller. Like you said,this is so new,there is so much not known for sure. It s mostly a ‘best guess’ kinda thing at this time.
Excellent work! As you say, it is important to consider breathability. Do you think fluid-resistance is important too? Disposable surgical masks have a fluid-resistant layer.
That’s a great question, Mike! We don’t expect these homemade face masks to be used long term, but either washed or replaced, so fluid-resistance isn’t something we’ve looked into yet. I would suggest that if you are concerned your mask has been contaminated or is wet, then you replace it with a new homemade mask as the safest option.
Outdoor-gear stores sell water-repelling compounds for applying to fabrics, some of which are breathable. Not sure how safe they are to breathe through. On the other hand, a surgeon may well get splashed in the face doing surgery; I am unlikely to be splashed buying groceries. Unless I go out in the rain without a broad-brimmed hat.
Would you mind sharing what type of HEPA filter you used? You did not refer to it as a hepa vacuum bag so I’m guessing it’s a filter for air conditioning? Some hepa products contain things we don’t want to breathe. Also paper towels come in such a wide variation. I don’t want to screw this up 🙂
The HEPA filter is a H11 HEPA filter for an air purifier – the Sqair air purifier, to be specific! It’s made from PP+PET fabric, not fiberglass.