PM2.5 refers to particles with aerodynamic equivalent diameter less than or equal to 2500nm in ambient air, also known as fine particles, which can be directly inhaled into human body, interfere with lung gas exchange, and cause asthma, bronchitis and cardiovascular diseases. PM2.5 mask refers to a mask that can effectively filter the invisible killers in the air, such as smog, viruses, bacteria, dust mites, pollen and other tiny particles, and also effectively filter PM2.5 particles. Suitable for environments with poor air quality. Whether the mask can effectively intercept PM2.5, its filtering material plays a decisive role, and the filtering principle of masks using different filtering materials is also different. From the history of filter materials, masks have experienced gauze cotton masks, medical antibacterial masks, activated carbon masks, meltblown cloth masks and film masks. At present, the mask with the best effect of preventing PM2.5 is the film mask, which mainly adopts the most advanced film material, and the fiber diameter is between 100~200 nm. The filtering principle is as follows: firstly, the membrane material with fiber diameter much smaller than that of PM2.5 particles in the air is adopted to ensure that the mask can effectively block PM2.5, viruses, bacteria and other particles in the air; Second, physical principles isolate air pollutants. As long as the membrane is not broken, the filtration efficiency of the mask can be ensured, and the mask can be longer and more durable (non-woven fabrics need to rely on static electricity to absorb particles because of their large fiber diameter, which is easily affected by temperature and humidity in the environment and will fail in a short time, so it can only be used once); Thirdly, nano-films have high hole uniform distribution rate and high moisture resistance. So that the film mask is more breathable and moisture permeable, and the wearing comfort is ensured.