Making sure you have a clean air filter is an easy way to protect against mold, odors and allergens. Micro filtration helps protect against allergens, pet dander, dust, pollen, mold spores and more. 18x20x1 air filter (actual size: 17-� X 19-� X ¾"). Merv 9 pleated 3-month high-capacity one-inch air filter. The high capacity series offers the lowest resistance, highest dust holding capacity and the longest service life. Merv 9 Filters dust, pollen, pet dander, mold spores, dust and sand so you will not breathe them in while inside your home or business. The high capacity series offers the lowest resistance, highest dust holding capacity and the longest service life. TRI-PLEAT ULTRA offers ultra low resistance 0.20”WG at 2000 CFM (for a 24x24x2) - this is up to 50% lower than comparable products. This equals a significant reduction in operating resistance which equals energy savings. The exclusive Ultra XT media features a unique fiber design that maximizes the amount of service area available to capture dirt particles allowing maximum efficiency at the lowest pressure drop - at the same time. Tri-Pleat Ultra utilizes a moisture resistance, robust two die-cut frame with diagonal supports bonded to the filter media pack for extra strength and to maintain proper pleat spacing. Filter frame is coated with Aqua Coat treatment for added moisture resistance. Up to 15 times more effective at capturing micro particles than ordinary fiberglass filters.