Replacement filter for Xiaomi Smart Air Purifier 4. High efficiency filter for filtering coarse particles such as PM 2.5, pollen, pet hair, etc. Activated carbon to remove unpleasant odors such as VOCs, cooking fumes, formaldehyde, smoke. Not suitable for Air Purifier 4 Lite and Air Purifier 4 Pro! Suitable only for Air Purifier 4!