5 Best Filter Inserts for Masks - Jan. 2021 - BestReviews
A cloth face mask must cover your nose, mouth, and chin, so a filter insert must be large enough to fit most of the face mask’s area. Avoid touching your face mask while wearing it. Don’t shift the mask around on your face. Choose a filter insert with a PM2.5 rating. It’s designed to filter particles smaller than 2.5 microns.