This air-conditioner filter traps dust, animal dander, pollen, and smoke particulates 20 times more effectively than ordinary air-conditioner filters. The electrostatically charged fibers trap allergen particles as small as 3 microns, while allowing the free flow of air. Lasts approximately two months. Measures 14" x 24"; simply cut to size with scissors for easy installation. May also be used as a heating vent filter.