<s>[INST] How do I choose what fabric mask to buy, or ideal fit and fabrics if I make my own? [/INST] 
Filtration, breathability and fit are all important.

If you purchase a non-medical mask, check the labels to make sure it complies with the ASTM F3502 standard or CEN/TS17553.

If you choose to make your own mask, it should be made of three layers of fabric:

Inner layer of absorbent material, such as cotton.
Middle layer of non-woven non-absorbent material, such as polypropylene.
Outer layer of non-absorbent material, such as polyester or polyester blend.
Watch the video on WHO’s recommended fabric mask materials and composition for more information.

For either type of mask, you should choose the one that fits your face well - cover your nose, cheeks and chin without leaving gaps on the sides. Masks with vents or exhalation valves are not advised because they allow unfiltered breath to escape the mask. Source: WHO. Link: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirus-disease-covid-19-masks. Field: Infectious Disease. Disease: COVID </s>