Charts are out there that talk about the level of protection based upon the fabric used. Tightly woven cotton quilting fabric is excellent, and they recommend three layers. Flannel is even better, and when I use it I use a layer of flannel and a layer of quilting fabric or muslin as the backing. Denim is also dense and very good. Masks block your sneezes and output, and if you wear it over your nose (as you should, but as many people don't) then you also are less likely to inhale moisture cast off by someone else in the vicinity, especially if that party is breathing through their nose over a mask or not wearing a mask at all.