Filtrete 14"x25"x1" Purple Ultra Allergen Pleated Furnace Air Filter. This filter is 90% effective at capturing large allergens like mold spores and pet dander, and electrostatically charged to capture microscopic allergens like dust, smoke, and smog. It 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, this filter lasts up to 3 months.