Filtrete 10"x20"x1" Purple Ultra Allergen Pleated Furnace Air Filter. It effectively captures 90% of large allergens like mold spores and pet dander, and electrostatically charges to trap microscopic allergens like dust, smoke, and smog. This filter also captures bacteria and particles that can carry viruses, meeting the guidelines of the American Lung Association Health House Program. With an MPR rating of 1500, it lasts up to 3 months.