Suppose an air purifier is marketed as having a True HEPA filter. In that case, it indicates that it satisfies the requirements of the US Department of Energy to filter 99.97% of bacteria, dust, pollen, and other airborne particles measuring 0.3 microns. Although they have not been tested to fulfill those criteria, filters marketed as HEPA-type or HEPA-grade may nonetheless be able to remove airborne particles.