The secret to the Austin Air Allergy Machine is the filter. The units are built with a pre-filter that surrounds a proprietary 3-stage filter. Featuring 60 sq. ft. of Medical-grade True HEPA filter paper followed by a layer of Military-grade HEGA (High Efficiency Gas Absorption) carbon cloth, providing an extremely large surface area for absorption of chemicals, gases, pollutants, viruses, odors and bacteria. So complete, this filter is certified to remove 99.97% of airborne particles 0.3 microns or larger in size and 95% of all particles down to 0.1 microns. No other personal air cleaner comes close. This is the Black replacement filter only, appropriate for the Black and Midnight Blue Allergy Machine units. Please note, this is the replacement filter only. The Allergy Machine Air Purifier is available separately. Replacement only requires work gloves and a Phillips-head screwdriver. While engineered to last for up to 5 years, an area having many pets, new carpeting, paint fumes, heavy smoking, urban pollution, photo studio, etc. will diminish the filter’s life. Cleaner air means better sleeping. The filters help lessen night-time allergies and asthma attacks which means fewer runny noses and cases of dry mouth. Leads to better health as the device filters chemicals, gases, viruses and bacteria, allowing immune systems to strengthen as coughing, wheezing and sneezing are reduced or eliminated. Keeping the filter working great is easy. Periodically vacuum the outside of the machine, clearing away the larger and most visible particulate matter and dust.