The Compatible Honeywell HAC-801 Replacement Filter for cool moisture humidifiers removes minerals and pollutants from water. Air Washing Prefilter helps capture dirt, dust, and pollen from the air that passes through the filter. Protec Antimicrobial Treatment helps prevent the growth and migration of mold, fungus, algae, and bacteria on the filter. The filter material is reinforced for maximum efficiency and longer filter life.