Masks do come in a number of sizes, and their sizes are primarily focused on the ability to filter out viruses or filter out bacteria. The size of virus particles released in the new diagnostic and treatment guidelines is now about 00.06-0.14 micrometers, so the more protective the mask is, the smaller the size of the virus that can be filtered must be. In fact, most of the virus is in the droplets, and the droplets are larger than the size of the virus, so many ordinary masks, such as ordinary medical masks or medical-surgical masks can already protect against viral contamination. But if in a very dense state, do not rule out the virus out of the droplets after the formation of crystals, may need to be more dense masks. N95 masks are very good protection, may filter more than 95% of the viral particles, the size of its filtered particles is 0.03 microns in size, is already smaller than the virus particles. Content source: Dr. Yurai