Replacement for Winix-Compatible Size 21 Air Filter & Cassette, Fits P300, WAC9500, WAC9000, WAC5000, WAC6300, WAC5500, WAC5300 & WAC5000B, by Think Crucial HIGH QUALITY AIR FILTER that can replace your Winix Size 21 Air Filter & Cassette. Get back to having a clean air to breathe again! HEALTHIER LIFESTYLE! No one wants breathe dirty air in their home and if you don't clean your air filter that will be exactly what you'll be doing! Replacing your filter will help clean your air purifier's air and allow for a healthier lifestyle! This filter helps keep our household dust, pollen and mold spores. This filter fits the following models: P300, WAC9500, WAC9000, WAC5000, WAC6300, WAC5500, WAC5300 & WAC5000B. EASY TO INSTALL so you can get back to breathing in clear air as soon as possible! Simply remove your old filter and put this brand new one in it's place! SAVE MONEY by using a new air filter! When your air purifier has a clogged or dirty air filter it can cause it to work harder which will end up hurting your electric bill! GUARANTEED SATISFACTION because of a 30 day full money bank guarantee and a trusted Think Crucial warranty. We are so confident in our products that we have no problem giving you every penny back if you're unhappy with your purchase. You won't see promises like that from big box brands!