The gradient structure of Blueair filters traps particles of all sizes while maintaining maximum airflow. It resists clogging and won't re-release particles back into the air, even when the filter is heavily loaded. Blueair filter media is ultrasonically bonded to prevent filter fibers and other particles from being added back into your environment. The only thing that comes out of our filters is clean air! 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. The Blueair Pro Replacement filter, Particle, keeps cleaning the air on average from 6 months to a year. The environment and fan speed will influence the actual life of the filter.