True Blue Allergen 18x20x1 Air Filter , MERV 11, 4-Pack 18 x 20 x 1 Pleated air filter Filters sub-micron airborne allergens like dust, dirt, pollen, pet dander, dust mite debris, microscopic allergens, smoke and smog Performance allergen reduction filter Lasts up to 120 days Minimum efficiency reporting value or MERV rating is 11