A top level air purifier should always equip with a HEPA filter. HEPA stands for High Efficiency Particulate Arrestance or High Efficiency Particulate Air. The key element for a HEPA filter is usually composed of an ultra-fine and glass-fiber material, which has to pass a filtration test to be certified as HEPA. Specifically, the United States Department of Energy (DOE) standard for HEPA filters requires a minimum 99.97 percent filtration of particles 0.3 microns in diameter. To differ from USA, the European Union has its own standard, EN 1822:2009, for HEPA certification. With this standard, HEPA filter is divided into several classes with filtration efficiencies ranging from 85% to nearly 100% for 0.3 μm sized particles. For most of filter, 0.3 μm sized particles are tough to be blocked, but HEPA filter would be able to remove over 99.97% of some types of particles that is smaller than 0.3 μm in the air. HEPA filters can block great amount of particulate matter that cause or aggravate asthma and allergies including:dust, pollen, soot, pet dander, dust mites, mold spores. HEPA filters can also make significant contribution on the reduction in spread of Covid-19. To learn more about HEPA filter with Top Rated Air Purifiers, please click here.