The secret to the Austin Air junior size air purifier units are their proprietary filter. The secret to keeping that filter clean and running smoothly is the Pre-filter. The long-lasting pre-filter traps large-sized particles such as dust, hair, soot and pet dander that can easily be seen with the eye during the first stage of Austin Air's multi-stage filtration process. In doing this job, the pre-filter helps to prolong the life of the inner filters, especially the HEPA filter. When combined with the layers of filter underneath, the entire unit 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 Pre-Filter only, appropriate for the Black and Midnight Blue Allergy Machine Junior, HeathMate Junior and HealthMate Plus Junior junior size Austin Air purifier units. These are also suitable for the Baby's Breath air purifier units. Please note, this is the replacement pre-filter only. The air purifiers and complete filter units are available separately. 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. 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.