Replacement filter C is for our AC5000 3-in-1 air cleaning system. This is a combination filter made of several layers of technology including: a charcoal filter to help decompose odors from smoking, cooking and pets; a True HEPA layer that captures 99. 99% of airborne particles such as dust mites, mold spores, pollens and pet dander; and a pre-filter that captures large dust particles, lint and pet hair. Filter should be replaced approximately every 6-8 months depending on use. HEPA replacement filter for GermGuardian model series: AC5000, AC5200, AC5300, AC5350 and Black+Decker model BXAP250. Pre-filter captures large dust particles lint and pet hair. Charcoal filter (aka activated carbon) contributes to the control and prevention of the growth of bacteria, germs and mold. True HEPA captures up to 99. 97% of airborne particles including dust mites, pet dander, mold spores, plant pollens and debris. Manufacturer recommends replacing filter every 6 months