is pm2.5 filter useful in preventing virus?
pm2.5 filter also called mask filter, anti haze mask filer, mask filter pad , activated carbon mask filter,  is usually used inside fabric face mask like below.

it contains 5 layer,  two layers Non-woven fabric, one layer activated carbon fabric, two layers nonwoven melt blown fabric .
the melt belown fabric inside can prevent virus efficiently .

from Amazon selling data, pm2.5 filter and activated carbon mask filter is becoming more and more popular in USA, Canada, Australia , Europe .

best pm2.5 mask filter now in market can achieve above 90% filteraion under 85L air flow. air flow is improtant in the filteration test, there are 32L air flow, 85L air flow etc., obviously 85L is a much higher testing standard than 32L.
it's important Amazon sellers and final consumers get real qualified products, only then mask wearing can be useful in the battle with covid19 virus.

Let’s work together and stay safe.