Here is a fast scientific paper, made with my colleagues, on handmade masks. We study the effects of liquid projections on some of them and propose a new way to disinfect them.
An interesting result is the following : ordinary handmade masks, made with 2 ordinary tissues, seem quite improved when one hydrophobic tissue is insert between the two. Hydrophobic tissue can be found in our housing : it can be a dust-proof Swiffer, a vacuum cleaner filter or everything else. A quite good one is a polyester fleece. To check if a tissue is hydrophobic, just put a water drop on it : if it stay there and isn’t absorb, it is hydrophobic !
UPDATE : I just learned the existence of this post, which is hopefully in agreement with our conclusions !