A real study on cloth masks with a good scientific design and instrumentation. It is a model system (not real virus) but it's the best I've seen to date. Takeaways: gaps around masks (used 1% gap, so very small) reduce their effectiveness by ~2/3. Tighter weave = better for cotton. Mixed fabrics cotton & chiffon or cotton & silk are better. Good numbers to use for effectiveness of a well-designed, reasonably well fitted cloth mask is ~35% effective. Also, if you're using an N95 as PPE, fit test it to make sure there aren't gaps (see lines 1 and 2 of the table) because cloth masks perform as well or better than an N95 with 1% gap (lines 2 vs 18). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834/