The new Size 21 Washable Ultimate Filter Cassette. This Filter Cassette offers 1 Full Year of Filtration in ONE easy to replace cassette. It includes a washable pre-filter, a 99.99% True-HEPA filter, our Washable Advanced Odor Control Washable Carbon Filter, and is treated with our Cleancel Anti-Microbial Coating. This Filter Cartridge fits comes standard in the U300 Signature Air Cleaner AND fits WInix Air Cleaner Models: P300, WAC9500, WAC9000, WAC5000, WAC6300, WAC5500, WAC5300, and WAC5000B.