News media like The New York Times and Today have been talking about using HEPA filters as a material to make DIY face masks. There are even YouTube videos showing how to DIY a mask out of a HEPA filter.
But just how well can HEPA filters capture virus-sized particles, and can HEPA filters be used to make an actual face mask? Let’s break this question down into four simpler questions.
1. Can HEPA Filters Capture Viruses?
Scientists have tested whether HEPA filters capture viruses by shooting viruses at the filters and measuring how many make it through. Those tests have found that HEPAs work great at capturing viruses.
In our DIY mask tests, we tested a H11 filter, and found it filtered out over 95% of virus-sized particles.
Read more: Can HEPA filters actually capture viruses? »
That means this H11 HEPA filter was able to filter out at least as much virus-sized particles as N95 masks. From this fact alone, HEPA filters seem like a perfect material to use for masks. However, there’s more to masks than just capturing particles.
2. Are HEPA Filters Breathable?
A critical question for making masks is breathability–how easy it is to breathe through a HEPA filter mask? If we can’t breathe through the mask, it’ll be uncomfortable to wear and we’ll likely take it off. The good news is that in Smart Air’s tests of over 30 DIY materials, the HEPA filter came out as one of the most breathable materials out there. The HEPA filter was about as breathable as a cotton t-shirt.
3. Is It Safe to Put HEPA Filters So Close to The Face?
Another critical question is whether it’s safe to put HEPA fibers next to our face and mouth. Some people have questioned whether fibers from HEPA filters break off, enter people’s lungs, and cause damage.
Read more: What exactly are HEPA filters and how do they work »
Scientists have tracked this with real HEPA filters and found that HEPA filters shed an insignificant number of tiny fibers when used in air purifiers. The number of fibers shed from HEPA filters are far fewer than the number of tiny PM2.5 particles in the air we normally breathe. In fact, the WHO PM2.5 limit is 35x more than from filter shedding.
Still, the tiny fibers may still be harmful to our health. Researchers have argued for both sides of the question, but a group of physicians in the US came to the conclusion that glass fibers like those used in HEPA filters should be considered “nuisance dust” and do not lead to permanent damage.
Read more: Can fibers break off from HEPA filters, and are they harmful to health? »
4. How Easy Is It to Shape HEPA Filters Into DIY Masks?
OK, so we know that HEPA filters are breathable and their impact to health may be limited. But how well can we actually make a mask out of HEPA filters? Synthetic polypropylene HEPA filters are made from two parts: the non-woven, particle-capturing part, and a stiff PET backing to give the filter its rigidity.
This stiff PET backing layer makes synthetic filters difficult to fold and and shape. If the HEPA is made from fiberglass, then it will be brittle. That presents a challenge.
Finally, HEPA filters present another challenge: unpleating. Almost all HEPA filters on the market are folded into a pleated HEPA design.
That improves their performance in air purifiers, but makes masking a challenge. Unfolding your HEPA filter may damage the filter, making it less efficient at capturing viruses.
HEPA filters are highly effective at capturing viruses and breathable too. An insignificant number of small fibers may break off the filters, but they are unlikely to cause permanent damage to health. Shaping the masks is possible but not easy because synthetic filters are fairly rigid, whereas fiberglass filters are too brittle.
WHAT NEXT?
Along with wearing masks, air purifiers with HEPA filters are also one of the best ways to stay safe from a variety of pollutants in our air including viruses and dangerous PM2.5. A recent CDC study confirmed significantly lower COVID-19 infection rates in schools that used HEPA air purifiers. HEPA filters can significantly lower the risk of a variety of deadly diseases including diabetes, heart disease, cancer, and high blood pressure.
Read More: Four Steps to Choosing the Best Air Purifier
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If I used the pleated material from a 3M Filtrete 2800 furnace filter, and cut it with scissors into a piece that would slide in between the layers of the best homemade mask materials you recommend, would that increase the ability of the mask to capture virus particles? The idea is that once you get that furnace filter apart, there is a lot of pleated material and it is very flexible and easy to breathe through. Then you could simply discard the filter material and wash the mask at the end of the day.
Can HEPA masks be washed & reused? Thanks
I’d like to follow up on the question about HEPA vacuum bag filters. How can we tell if there are glass fibers or meltblown? I’ve heard they are unsafe due to the potential to have glass particles inhaled. I’ve also heard that HEPA vacuum bags don’t have any fiberglass. Then the articles says that even if it does, it’d likely be “nuisance”. So, clearly results show it filters well. The question is very simply are HEPA vacuum bags safe as mask inserts or not? Thanks,
It is not true that HEPA filter is breathable (easily). I sealed the filter around my face to see if I could actually breathe in and out, and HARDLY any air was coming in or out, because it is so tightly messed. So the air I breathe in and out once I put the filter in a re-usable mask, is really coming from around the perimeter of the filter and mask. That’s what I realized. Please try breathe through the filter, and you will know what I’m talking about.