The Nordic Pure MERV 13 anti-allergen pleated air filter is the ideal filter to reduce airborne contaminants in your home or business. With each pass through your MERV 13 air filter, the air in your environment improves. This electrostatic air filter attracts and captures airborne dust, pollen, mold spores, pet dander, smog, dust mite debris, smoke and bacteria. The MERV 13 anti-allergen pleated air filter is made of synthetic material that will not support the growth of mold and bacteria. The MERV 13 high efficiency air filter will attract and capture the small, allergy-aggravating micro-particles that can cause your family discomfort. The Nordic Pure anti-allergen pleated air filter has a Minimum Efficiency Reporting Value(MERV) of 13 which means that it will collect more than 90% of 1.0-10.0 microns of contaminants and up to 95% of .30-1.0 microns of contaminants. Particles in indoor air are measured in microns, which are 1/1000 of a millimeter. A human hair is about 70 microns wide. The MERV 13 anti-allergen pleated air filter is comparable to a filter with a MPR rating of 2200 and is a great start to creating a healthy environment. Nordic Pure air filters have an actual size that is a fraction of an inch smaller than the nominal size. With the 4" and 5" 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 13 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.