HEPA filters have been mentioned as a possible fabric material for making 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? In this article, we’ll get to the bottom of whether HEPA filters make effective homemade face masks.
Let’s break this question down into 3 parts:
What are HEPA Filters Made From?
HEPAs are air filters traditionally used in air purifiers or central air systems to clean indoor air. They’re made from a mat of randomly aligned fibers – either polypropylene (PP) or fiberglass. Polypropylene is similar to the material in a sports t-shirt. Fiberglass Here’s a closeup of the HEPA filter Smart Air makes for The Sqair air purifier, it’s made from PP.
How Well can HEPA Filters Capture Virus-sized Particles?
Read more: Can HEPA filters actually capture viruses? »
That’s great! The H11 HEPA filter we tested was able to filter out the same percentage of virus-sized particles as an N95. On the surface, HEPA filters might seem like a perfect material to use for masks, but there’s more to it than just particle capture effectiveness.
Will HEPA Filters Make Effective Face Masks?
To answer this question, we need to look at more than just the effectiveness of HEPA filters at capturing viruses. It’s important to consider how easy it is to breathe through a HEPA filter mask. Also, we should consider the health risks from having HEPA filters close to the face and mouth. Finally, can HEPA filters actually be shaped into a well-fitting homemade face mask?
Breathability of HEPA Filter Face Masks
Breathability is important. 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.
Is it Safe to put HEPA Filters so Close to the Face?
Data shows that HEPA filters can 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. Studies are inconclusive, 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.
How Well can a HEPA Filter be Turned Into a Mask?
OK, so we know that HEPA filters are breathable and their impact to health may be limited. That’s great! 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. Fiberglass filters are also brittle by nature, since they’re made from glass fibers.
Finally, almost all HEPA filters available on the market are folded into a pleated HEPA design. That gives them better performance when used in air purifiers. Unfolding your HEPA filter may well cause destructive damage to the filter, making it less efficient at capturing viruses.
Bottom Line on Homemade DIY Face Masks Made Using HEPA air Filters
HEPA filters are highly effective at capturing viruses, and also breathable too. An insignificant number of small fibers may break off the filters, but they are unlikely to cause permanent damage to health. Synthetic filters are fairly rigid and difficult to shape, whereas fiberglass filters are too brittle. Making masks out of HEPA filters is possible, but not easy to get right.
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.