I keep reading this argument, that the virus is 300 nm hence a filter doesn't cut it. Let's clarify that the virus is not flying around by itself, 300 nanometers in diameter. They are attached to spit particles which are much larger. 10 um and up. Most are 100 um and up.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2843952/
So
a) an N95 mask will totally cut these particles and protect you to a high level
b) we are starting to wear face masks because we want to keep the spit IN
G