XPost: sci.misc
No mask is 100% effective. An N95, for example, is named as such
because it is at least 95 percent efficient at blocking airborne
particles when used properly. But even if a mask has an 80%
efficiency, Marr said, it still offers meaningful protection.
...
...
Marr said research shows that high-quality masks can block particles
that are the same size as those carrying the coronavirus. Masks work,
Marr explained, as a filter, not as a sieve. Virus particles must
weave around the layers of fibers, and as they do so, they may crash
into those fibers and become trapped.
https://www.cbsnews.com/news/face-mask-effectiveness-what-science-knows-now-60-minutes/
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