The Blue Pure 311 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 vs. the same models with only mechanical filtration (H13 filter), the Blue Pure 311 Particle and Activated Carbon Filter lasts longer, on average 6 months. 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.