Certified hepa filter captures up to 99.97Percent of microscopic allergens and 99.9Percent of certain bacteria and virus from the air that passes through the filter, 0.3 microns and larger For best performance replace HEPA filter(s) once per year Fits Honeywell doctors choice true hepa air purifier models: Hpa020 and Hpa030 series Package contains one hepa filter To ensure stated product performance, use only certified Honeywell replacement filters