When purchasing masks, we often come across 3 key specifications that help indicate how effective the mask is - PFE, BFE, and VFE.
Simply put, these numbers who how effective the product is against filtering particles, bacteria, and viruses. All legitimately produced masks are tested by independent laboratories to ensure it is actually effective, the most popular being Nelson Labs and SGS.
Most masks test against particles, viruses, and bacteria using ranges between 0.1 to 3 microns.
Particulate Filtration Efficiency (PFE)
This describes a mask's filtration efficiency when it comes to particles, including dust, pollution, and even viruses and bacteria. It's an efficiency rating for filtering particles of various sizes, and normalized to an average percentage. Of course, there are different efficiency levels for various particle sizes, as illustrated by this chart: