Product Description The Flanders NaturalAire Pre-Pleat 40 Charcoal Air Filter features a synthetic fiber filtering medium that is laminated to an expanded metal backing for strength. This combination is then folded into an accordion pleat arrangement to increase filtering surface. This greater filtering surface allows more effective filtration while keeping airflow resistance low during its 90-day service life. The media pack is encased and sealed within a die-cut, moisture resistant frame. Performance level is MERV (Minimum Efficiency Reporting Value) 6, providing filtration against many airborne particulates found in indoor air. From the Manufacturer Flanders NaturalAire PrePleat MERV 6 utilizes the latest technology in fine mesh activated carbon. It is formulated to increase the attraction and capture of pet and human odors, as well as other common household contaminants that are known to aggravate allergies.