Nordic Pure 12x18x1 MERV 7 rated pleated air filters 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 filter, lint, household dust, pollen, dust mites, mold spores and other contaminants are removed. Our treated synthetic filter media prevents the growth of bacteria or mold, resulting in a much healthier living space. MERV 7 air filters are comparable to air filters with the MPR rating of 500-600 or FPR rating of Green. Particles in indoor air are measured in microns, which are 1/1000 of a millimeter (a human hair is about 70 microns wide). Each Nordic Pure 1” MERV 7 air filter captures airborne particles as small as 3.0 to 10.0 microns. This high performance air filter will outperform non-electrostatic fiber-glass filters, washable filters, poly disposable filters, and will help keep your air conditioning and heating systems running efficiently, saving you money on utilities and costly maintenance. The effective life of your air filter depends on both the inside and outside conditions in which you live. We recommend that you change your air filter every 30-90 days to maintain maximum efficiency and economy.