The Blueair 400 Series Particle Filter utilizes HEPASilent technology to remove harmful particles from the air, such as pollen, dust, pet dander, and bacteria. Using electrostatic and mechanical filtration, Blueair purifiers filter out indoor pollutants with 99.97% accuracy down to 0.1 microns in size. The thermally bonded polypropylene and polyethylene filter fibers are naturally free of chemicals, naturally antibacterial, and fiber shedding resistant. The gradient filter structure is less dense than other filters, allowing Blueair purifiers to achieve greater airflow with lower air pressure and a quieter, more efficient clean air delivery. The Blueair 400 Series Particle replacement filter is made with materials that are 100% recyclable, so you’ll only add clean air back into your environment. Recommended filter change: every 6 months when used 24 hours a day.