Nordic Pure 20x24x4 MERV 15 Plus Carbon air filters are made of electrostatically charged synthetic materials with an added flat panel infused with activated charcoal that will attract and capture most airborne particulates in your home. Odorous gases and vapors (VOC) are attracted to and held by the activated carbon material while maintaining excellent air flow properties. All Nordic Pure + carbon pleated air filters are manufactured using a heavy duty, moisture resistant beverage board frame. There is a metal mesh support grid bonded to the pleats for extra support. MERV 15 furnace air conditioner filters are comparable to HVAC filters with the rating of MPR 2800. It is important to note that because of this high filtration and air flow restriction, HVAC systems should be rated to handle filters of MERV 15 and above. Nordic Pure MERV 15 air filters work great in newer, high efficiency systems that use HEPA filters. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and economy.Important Note: Almost ALL furnace filters have a different "actual size" than the nominal size printed on the air conditioner filter. It's best if you measure your air filter for the EXACT size and compare it to our "Actual Size" - and then you can be sure your A/C air filter fits!