The Air King 9900 20 Inch Box Fan takes in unfiltered air and cleans it to provide clean air throughout an entire room. The amazing features included with the 9900 include:Home Air Filter Comes complete with one pleated home air filter. Durable Construction The guard is made of impact resistant plastic and the propeller is constructed of polypropylene. Adjustable Speeds and Filtration Volumes Features 3 speeds and filtration volumes for completely customizable air circulation and purification. Beneficial to Allergy Sufferers Filters dust, smoke, pollen, pet hair and spores which are harmful airborne particles.