Important Note: Almost ALL furnace filters have a different "actual size" than the nominal size printed on the air filter. It's best if you measure your air filter for the EXACT size and compare it to our "Actual Size". With the 4" and 5" air filters there is a wider variance depending on the manufacturer. Nordic Pure Honeywell Replacement MERV 12 rated air filters are traditional 5” filter at an actual 4 3/8”. You should always measure your current filter or the housing to make sure the actual size correlates with the filter you are ordering. Nordic Pure pleated air filters are manufactured using a heavy-duty, moisture resistant beverage board frame. There is a metal mesh 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 filters are comparable to HVAC filters with the rating of MPR 1500-1900. This high-performance HVAC replacement filter will help keep your air conditioning and heating systems running efficiently, saving money on utilities and costly maintenance. The effective life of your AC air filter depends on both the inside and outside conditions in which you live. It is important to regularly change your furnace air filters especially during any home improvements for fresh, clean air in your home or office. We recommend that you change your air filter every 3-6 months to maintain maximum efficiency and economy. From the Manufacturer 20x20x5 Honeywell Replacement MERV 12 Pleated Furnace Air Filter Box of 1 - Manufactured by Nordic Pure.