Filter-Monster branded replacement True HEPA replacement filter compatible with Blueair 400 Series Particle Filter. This filter is engineered to be compatible with Blueair Classic Air Purifier Model 402, 403, 405, 410, 450E, 455EB, 480i. To maintain peak performance, and fresh air in your home it is recommended to replace every six (6) months or more often depending on air quality and environmental factors. Package contains three (3) filters.