1. Compatible: Compatible with Blueair 411i Max and 411a Max air purifiers. Premium Blue Pure F4MAX replacement filters for the 411i Max series. Not compatible with 411, 411+ and 411 Auto. 2. 2-in-1 Filtration: These 411i Max filters for Blueair 411i Max and 411a Max air purifiers combine 2-in-1 HEPASilent and Carbon dual filtration technology to deliver more clean air, faster, with less noise and energy consumption than HEPA filtration alone. 3. Premium F4MAX Filters: The 411i Max HEPA filter removes at least 99.97% of particles as small as 0.1 microns, such as pet dander, pollen, dust, common pollutants and fabric fibers; the Carbon filter absorbs household odors from smoking, pets and cooking. 4. Excellent Quality: We provide high-quality and durable filters for 411i Max and 411a Max air purifiers to extend the filter life. To improve the performance of the air purifier, please replace the filter every 6 months.