Whirlpool 817100, 4-Pack, 1-Full Year Supply Charcoal Carbon Pre-Filters For Portable Tower Model APMT2001M, 3.9x11 inch Package contains 4 new replacement filters  one full years Supply Filters are Carbon-Based removing larger particles and unpleasant odors. Improves and maintain clean fresh air quality in the house. Fits Whirlpool Model: APMT2001M Recommend to Replace Filter every 3 Months.