Although not a “submicronic” air cleaner, the Fantastic Filter® effectively removes airborne particles down to 1.8 microns and is the minimum requirement for any heating and cooling system. Designed by leading allergy and asthma physicians, this top-rated one-inch filter is constructed of Polyolefin which prohibits the growth of bacteria, mold, mildew or fungi in normal residential applications. Each Fantastic Filter provides 60% greater particulate loading capacity and allows for much better air flow than high-end store-bought filters. The Fantastic Filter needs to be changed four times a year under normal residential conditions. Includes 4 filters. Sizes 12x20, 12x24 and 24x24 are 1/4" under nominal. All other sizes are 1/2" under nominal.