This hybrid exhaust filter combines a Certified S-Class HEPA Filter with a thin layer of Activated Charcoal to provide simultaneous HEPA filtration and trapping of unpleasant odors. It should be replaced every 12 months with typical household use. The completely sealed systems in Miele Midsize and Fullsize Canisters, when equipped with Active Certified S-Class HEPA Filters, will retain 99.97% of pollens, household dust, dust mite droppings and other allergens as small as 0.3 um in size. This filter is highly recommended for those who have dust related allergies or asthma. This filter fits in the same place as the Active Air Clean or Super Air Clean Filter. You can not use more than one exhaust filter at the same time.