The Guardian Technologies True HEPA Filter B Pet is a combination filter that incorporates multiple layers of filtration including: a pre-filter, a charcoal filter and a True HEPA filter, to help improve indoor air quality. The PetPure Treatment is an antimicrobial agent added to the filter to inhibit the growth of mold, mildew and odor-causing bacteria on the filter surface. True HEPA captures 99.97% of allergens including pet dander, dust mites and pollen. For use with 3-in-1 Air Cleaning System 22inch and 3-in-1 Digital Air Cleaning System w Pet Pure Filter - 22inch (sold separately). It is recommended that the filter be replaced every 6-8 months depending on use. Materials: Pleated Paper. Dimensions: 15.77"L x 4.76"W x 1.29"H; 0.35 lbs.