I got curious about if home made cotton masks were actually useful and found these two studies that say they aren't as effective but better than nothing

https://www.ncbi.nlm.nih.gov/pubmed/24229526 
https://www.ncbi.nlm.nih.gov/pubmed/18612429 

DIY cotton masks absorb a lot of moisture so it might be a breeding ground. Remember to sterilize.

This thread is for N95 masks specifically but heat is probably the best sterilization method to ensure moisture droplet blocking capability https://twitter.com/FioraAeterna/status/1233850778974068736