Thread by @peterktodd

Good summary of some actual science on masks:

1) Very effective at protecting you from the flu: 75% risk reduction for parents taking care of sick kids.

2) Surgical masks and "proper" N95 masks are almost equally effective.

Why? Well...

smartairfilters.com/en/blog/n95-ma…

While virus particles are really small, the flu and coronavirus are probably mostly spread by droplets, which are quite large. Ever tried breathing mist through a cloth? It gets filtered out just fine.

Secondly, while surgical masks don't fit perfectly, they fit pretty well.

If a mask filters 90% of the air you breath - w/ 10% bypass at the edges - you're still breathing in 90% less droplets. It's likely that a single unlucky droplet is enough to infect you, so that's probably something like 90% less risk of _that_ infection mechanism.

Even surgical masks are pretty good at filtering particles of all sizes. Eg one test found 80% of ultra-small diesel exhaust particles were filtered out. Which isn't surprising if you know how HEPA filters actually work. Hint: they're not a sieve.

smartairfilters.com/en/blog/corona…

These guys also reported on some actual fit testing, and found that the N95 masks they tested fit just fine out of the box with little effort, with a real world of mostly 95%+ filtration. Doesn't surprise me: if they didn't work, industry would fix them.

smartairfilters.com/en/blog/corona…

Finally, all masks probably remind you not to touch your face.

If you don't want to do your homework, here's a great explanation of how HEPA filters actually work, why they can filter nanoparticles like diesel exhaust just fine (way smaller than viruses), and why even a simple piece of cloth is ~30% effective.

smartairfilters.com/en/blog/can-he…