Austin Air FR402A Bedroom Machine Replacement Filter, BlackSTAGE 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 odors STAGE 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