DIY face masks with nylon stocking on top can work better than surgical masks

> As has been previously observed by Cooper et al. (1983), adding a layer of nylon stocking over the masks minimized the flow of air around the edges of the masks and improved particle filtration efficiency for all masks, including all commercial products tested. Use of a nylon stocking overlayer brought the particle filtration efficiency for five of the ten fabric masks above the 3M surgical mask baseline.

> When compared to commercial baseline masks, the addition of the stocking layer improved particle removal efficiency of many masks to match or exceed the baseline; the masks that achieved this level of filtration using the stocking layer each included a filter layer (organic cotton batting, Pellon, or loosely-woven cotton muslin) in addition to two layers of cotton fabric.

I think we now have a basic recipe for producing good home-made masks!

Also, some sewers did tests with the same machines used in this article. Their design claimed 50% efficiency without any filtration media. Adding filtration media achieved up to 87%, equivalent to the best results in this study, by using particular brands of blue shop towels. I think their good results are because their design also emphasizes creating a better seal to the face. https://suayla.com/pages/suay-community-mask-coalition