STAGE 1 - Large Particle Pre-filter. Removes particles easily seen by the naked eye (e.g. dust, hair and pet dander)STAGE 2 - Medium Particle Pre-filter. Removes small to medium size particles (e.g. molds, spores and pollen)STAGE 3 - 60 sq. ft. of True Medical Grade HEPA. Removes 99.97% of all particles larger than 0.3 microns and 95% of all particles larger than 0.1 microns.STAGE 4 - Military Grade HEGA Carbon Cloth. HEGA (High Efficiency Gas Arrestance), providing an extremely large surface area for adsorption of chemicals, gases, viruses and bacteria.Replacement filter for the Austin Air Allergy Machine. The Austin Air AllergyMachine was developed specifically for people with asthma and allergies. Itsunique design increases air flow, filtering allergens from the airimmediately. In clinical trials the Austin Air Allergy Machine was shown todramatically reduce hospital visits for young asthmatic children. All standardsize units are interchangeable with all standard size filters.