A HEPA, or High Efficiency Particulate Air, filter is a technology found in some room air purifiers that removes more than 99% of all airborne pollutants 0.3 microns or larger from air that passes through the filter.
HEPA filters are found in a number of ENERGY STAR certified room air purifiers but are not a requirement for a purifier to earn the ENERGY STAR. ENERGY STAR certified room air purifiers may also use ionizers or electrostatic precipitators to remove pollutants from the air.