At present, there are mainly 4 kinds of common masks. One is surgical masks. It is made of three-layer non-woven fabric, suitable for operating room environment, and can block particles with a diameter of about 4 microns or more. The second is activated carbon medical masks. Adding activated carbon materials, the main function is to isolate the smell, not to prevent bacteria and viruses. The third is dust masks. The main function is dust-proof and general anti-bacterial function. The fourth is ordinary paper masks. It is useful for blocking larger particles. Viruses smaller than 5 microns in diameter can pass easily, and the function of separating bacteria is limited.
N95 respirator is one of the nine types of dust respirators certified by the National Institute of Occupational Safety and Health (NIOSH). N means that its material is only suitable for filtering non-oily dust, and 95 means that its filtering effect can reach at least 95%.