Capable of capturing particles invisible to the naked eye, HEPA (High Efficiency Particulate Air) Cartridge Filter meets industry standards for HEPA air filtration by providing filtration of 0.3 microns @ minimum of 99.97% efficiency. Ideal for working with allergens, powders, and superfine particles. Cloth Pre-Filter Bag provides extra stage of filtration extending cartridge filter life. Fits all Guardair 55, 30, and 20 Gallon Drum Vacuums and Vacuum Generating Heads.