Filtrete 14"x20"x1" Purple Ultra Allergen Pleated Furnace Air Filter. It effectively captures large allergens like mold spores and pet dander, as well as microscopic allergens like dust, smoke, and smog. This electrostatically charged filter also captures bacteria and particles that can carry viruses, meeting the guidelines of the American Lung Association Health House Program. With a MPR rating of 1500, it lasts up to 3 months.