The Fellowes replacement True HEPA Filter captures 99.97% of particles and impurities as small as 0.3 microns, including mold spores, pollen, dust mites, most airborne microbes, allergens and cigarette smoke. Filter is compatible with the Fellowes PlasmaTRUE Medium Air Purifier. Replace the True HEPA filter approximately every 12 months in order to ensure that the Air Purifier continues to operate effectively.