The Blue Pure 311 Auto Particle and Activated Carbon Replacement Filter protects against both gaseous and particulate contaminates. An activated carbon mesh layer eliminates harmful gaseous pollutants such as volatile organic compounds (VOCs), tobacco smoke, and other odors. In addition, advanced polypropylene filter media removes particle pollutants down to 0.1 micron in size from your indoor air, such as pollen, dust, and pet dander. Using a 360-degree air intake and up to 4 times the filter surface area than competing replacement filters, the Blue Pure 311 Auto Particle and Activated Carbon Filter lasts longer, on average from 6 months to a year. Subscribe & save up to 10% on auto-delivered filters when replacement is needed; We recommend replacing your filter about every 6 months depending on usage. NO COMPARISON – 4X FILTER SURFACE AREA & 360 AIR INTAKE: Blueair models with HEPASilent's mechanical and electrostatic filtration produced higher CADR, lower noise, and had lower energy consumption vs. the same models with only mechanical filtration (H13 filter). *Tested on E.coli, Influenza A (H1N1), A.niger with a minimum reduction rate of 99.9% in 60min.