Why might homemade face coverings be more effective than expected? Sharing preliminary results from @isjinpan and @charbelEharb because of importance. All masks on manikin, even loose bandana, have ~50% or better efficiency for droplets/aerosols 2-5 microns. /1

This is for inward protection. Efficiency is much lower and highly variable, as expected, for droplets/aerosols <1 micron (results still in the works). If transmission is dominated by droplets/aerosols >1 micron (see my earlier posts), then almost any cloth mask is helpful. /2

Even if our masks are 50% effective, we get 75% reduction in exposure if both people are wearing them. Distancing reduces this a ton more, and ventilation helps, too. And https://www.nytimes.com/2020/05/29/health/coronavirus-transmission-dose.html /3