Nordic Pure 20x20x4 Pleated Air Filters MERV 12 are made of electrostatically charged synthetic materials that attract and capture most airborne particulates in your home. Each time air passes through a Nordic Pure pleated furnace filter, lint, household dust, pollen, dust mites, pet dander, smoke particles, virus carriers, bacteria, allergens, mold spores and other contaminants are removed. 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.