The Nordic Pure MERV 15 hypoallergenic pleated air filter is a high efficiency air filter designed to reduce all airborne contaminants in your home or business. This electrostatic air filter attracts and captures airborne dust, pollen, mold spores, pet dander, smog, dust mite debris, smoke, carbon dust, sea salt, and bacteria. The MERV 15 hypoallergenic pleated air filter is made of synthetic material that will not support the growth of mold and bacteria. This MERV 15 high efficiency air filter will attract and capture the small, allergy-aggravating micro-particles that can cause your family discomfort. The Nordic Pure hypoallergenic pleated air filter has a Minimum Efficiency Reporting Value(MERV) of 15 which means that it will collect more than 90-Percent of ALL microns of contaminants. Particles in indoor air are measured in microns, which are 1/1000 of a millimeter. Because of this high filtration and air flow restriction, heating and air conditioner systems should be checked to make sure they can handle filters rated MERV 15 and above. Nordic Pure air filters have an actual size that is a fraction of an inch smaller than the nominal size. With the 4-Inch and 5-Inch air filters there is a wide variance between the nominal size and actual size. Almost ALL filters have a different actual size than the nominal size printed on the filter so it is best if you measure your filter for the EXACT size and compare it to our "Actual Size. This is why we ask you to measure your filter so you aren't surprised if the filter doesn't fit! Our MERV 15 four or five inch air filter should be changed at least every 6 months depending on your environment. Changing your air filter at the recommended time will help maintain a healthy environment as well as keeping your air conditioning and heating systems running efficiently.