Airpura Replacement Carbon Filter for AirPura Models R600, UV600, P600, P600+ 18 Lb., 2 Inch Carbon Filter Airpura carbon filters adsorb airborne chemicals to ensure the safest air possible. Replace the carbon filter at least every 2 years. More frequent replacement may be required depending upon the airborne chemicals and the chemical levels being filtered. This two inch thick, 18 pound carbon filter fits Airpura Air Purifiers 600 series models R600, UV600, P600, and P600+ Air Purifiers.