Designed for the Alen A350 and A375 Air Purifiers (Visit alencorp.com for details), the Alen HEPA-Silver Filter combines three layers of filter technology to purify and freshen the air in your home while protecting the filter against bacteria and microbes. 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 style material that attracts and captures dust, pollen, pet dander, mold spores and other airborne pollutants. Alen"s anti-microbial Silver-Ion threads are woven into the HEPA style material, protecting the filter from harmful bacteria* and microbe growth. In the final layer, clean air passes through a layer of Alen"s Activated Carbon, reducing light odors and chemicals commonly found in the air from cleaning products, smoke, cooking, pets and various other household materials. *Test results demonstrate a 99.99% kill rate on E. Coli and Staph Bacteria.