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Comment by dataangel | Hacker News Reader

what variability? AFAIK in controlled studies masks work (as in when you actually test things in a lab rather than looking at population statistics), are more effective when both people in the room are wearing them, we know the size of particle they filter and we know the viruses are bigger than that. there's 0 doubt at this point they do what they are supposed to do.

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I'm talking about variability in the studies on population-wide masking. The consistency in lab studies is a major part of why I belive masking is an effective public health measure but would like more study on what's causing the variation in ecological studies.

> we know the size of particle they filter and we know the viruses are bigger than that.

If we're talking cloth masks as most people are, the viruses are actually way smaller.

Do viruses float freely in the air, or are they mostly in aerosolized bodily fluids when from an infected persons coughs and sneezes? Cloth masks are great at trapping those and greatly reducing the "muzzle velocity" of droplets that do escape.

Yes, this is the key insight. The mere fact that the virons are smaller than holes in the mask means nothing. The virons aren't expelled from our mouths or noses on their own, but are attached to moisture droplets which _are_ effectively trapped by surgical (and better) masks.

During mid covid I did a demo for my kids. A sheet of paper and a spray bottle.

Test 1, spray from 2 feet. Of course the paper was soaked.

Test 2, a cloth mask placed on the paper. It gets damp, especially if left in place.

Test 3, a cloth mask over the spray bottle. The mask blocks almost all of the spray.

We did not bother with test 4 (2 masks) after the 3rd, but I think they understood the point.

We did retry 3 with a medical mask, with 0 spray through.

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