I use these filters to make masks to protect against COVID-19. Unfolded and flattened it yields a usable 60" x 19" filter cloth. I cut out oval filters from 4.5" x 4.5" areas using a template that fits the silicone mask I'm using (NXTGEN Automotive reusable HEPA filter face mask, available from Revain). In fact, I tripled the filters to improve the sound quality after MERV 14 without any noticeable effort of breathing. MERV 14 is >75% efficient for 0.3-1.0 micron particles and >90% efficient for 1.0-3.0 micron particles. In theory, three filter passes (three layers) should be >98% efficient for 0.3-1.0 micron particles and >99.999% efficient for 1.0-3.0 micron particles, but in practice this is likely, not certain so. The Covid-19 virus is about 0.125 microns in size, but research says it's almost always transmitted in droplets larger than 1 micron. So my solution should offer some security.
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