STAGE 1 Large Particle Pre-filter. Removes particles easily seen by the naked eye (e.g. dust, hair and pet dander)STAGE 2 Medium Particle Pre-filter. Removes small to medium size particles (e.g. molds, spores and pollen)STAGE 3 Over 780 cubic inches of Activated Carbon and Zeolite Removes chemicals, gases and odorsSTAGE 4 60 sq. ft. of True Medical Grade HEPA. Removes 99.97% of all particles larger than 0.3 microns and 95% of all particles larger than 0.1 microns.Replacement filter for the Austin Air Bedroom Machine. The Austin Air BedroomMachine is designed to help those who suffer from various sleep-relatedproblems. The results of two separate clinical trials show this unit to behighly effective at removing dangerous airborne pollutants from the home. Keepthe air in your bedroom free from pollution and get the good night’s sleep youdeserve.