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.
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.
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.
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.
Paddy is the CEO of Smart Air, running operations from Beijing. He has a Masters in aeronautical engineering from Bristol University, UK having specialised in aerodynamics. An advocate for open data, free information and transparent business, he spends his spare time promoting honest business and social enterprise.