3M masks sold in the market can be divided into several varieties, respectively, warm masks, anti-particle masks and medical masks. 3M warm masks are mainly used to keep warm, and usually do not protect against viral infections. 3M medical masks, mainly used in hospitals, epidemic prevention stations and other workplaces, can not only isolate blood, body fluids, secretions, etc., but also effectively protect against viral infections. The common 3M masks on the market are generally anti-particle masks, which can block coronaviruses.3M anti-particle masks are divided into several filtration levels, which are 90%, 95% and 99.97%, etc.. In the mask marked as KN90, KN95 is the degree of filtration of the mask, of which KN95 masks are suitable for the prevention of smoke, dust and pathogenic microorganisms. To prevent new coronavirus infection, you can select masks with filtration degree of KN95 and above.