Important Note: Almost ALL furnace filters have a different "actual size" than the nominal size printed on the air conditioner filter. Its 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! With the 4" and 5" air filters there is a wider variance between the nominal and actual size depending on the manufacturer. Nordic Pure 20x25x5 Honeywell Replacement MERV 12 rated air filters are what is considered the traditional 5” filter at an actual 4 3/8”. The Pleated Plus Carbon air filters are made of a dual material where the MERV rated material has been fused together with a carbon layer. Odorous gases and vapors (VOC) are attracted to and held by the activated carbon material while maintaining excellent air flow properties. All Nordic Pure 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. Our AC filter media prevents the growth of bacteria or mold, resulting in a much healthier living environment. MERV 12 furnace air conditioner filters are comparable to HVAC filters with the rating of MPR 1500-1900. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and economy.