A true HEPA filter is a High-Efficiency Particulate Air filter.  HEPA filters are used to clean the air in airplanes and hospitals. HEPA filters remove 99% or more of airborne pollutants like mold, bacteria, pollen, dust, pet dander, etc. The Puremidifier’s HEPA filter will remove 99% or more of particles that are 2.5 microns or larger.