AFAIK at best it depends upon number of layers, what kind of layers, fit, droplets (and size) vs. aerosols, humidity, interpersonal distance and dwelling time, and of course ventilation. Given the framing of the "mask debate" in the US with essentially no frequent or defining mention of face covering quality/qualities, essentially it seems like Cargo-cult science at the restrictions/policy level. There are people who meet the requirements essentially breathing through stretched or O(500um) single-layer mesh.

I have not looked closely enough at electret properties to know if meshes with larger pore sizes can really stop 0.06um virus particles. (Or 10nm according to this https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-C... )