Designed for the Alen BreatheSmart HEPA air purifier, the Alen HEPA-Fresh Plus filter combines three layers of filter technology to purify and freshen the air in your home. Polluted air first passes through Alen's washable pre-filter to capture large particles, extending the life of the filter. In the second layer, air moves through a unique, electrostatically charged HEPA type material that attracts and captures dust, pollen, pet dander, mold spores and other airborne pollutants. In the final layer, clean air passes through a thick layer of Alen's activated carbon (3 lbs. ), reducing odors and chemicals commonly found in the air from cleaning products, smoke, cooking, pets and various other household materials. Medical Grade H13 True HEPA layer that captures 99.99% bacteria, aerosolized viruses, and airborne particles larger than 0.1 micron.