Blue Pure 121 Replacement Filter, Particle and Activated Carbon, Fits Blue Pure 121 Air Purifier, by Blueair It is important to only use genuine Blueair replacement filters to maintain optimal performance and warranty. Filters that are not Blueair genuine will void your units warranty. GENUINE Blueair Replacement Filter for Blue Pure 121 PARTICLE and HEAVY DUTY ACTIVATED CARBON filter reduces pollen, dust, pet dander, mold spores, bacteria, odor, VOCs, Tobacco smoke and other gaseous pollutants. RECOMMENDED to change filter once every 6 months, or dependent on usage. This filter is eco-friendly and can be recycled after it's changed.