https://slatestarcodex.com/2020/03/31/ssc-journal-club-macintyre-on-cloth-masks/

Content warning: this is a complicated analysis of something people care about a lot right now. I'm not confident in my analysis, the post comes to no clear conclusion and there are no easy answers about how to proceed. If I see this on Twitter with some headline about it DESTROYING somebody, I am going to be so mad.]

The New York Times says that It's Time To Make Your Own Face Mask. But MacIntyre et al (2015) says it isn't.

The surgical masks used in hospitals are made out of non-woven fabrics that are pretty different from anything you have at home. But in some developing countries, health care workers instead use masks made of normal cloth. Laboratory tests find that improvised cloth masks block 60 – 80% of virus particles. Respirators and real surgical masks block 95%+, but 60-80% still seems better than nothing. And most of the masks ordinary people wear in Asian countries are cloth, and they seem to do pretty well. So there's some circumstantial evidence that these cloth masks might be helpful. Most experts in the early 2000s agreed that these masks were probably better than nothing. In 2015, an Australian team set out to prove it with a randomized controlled trial.