Tier1 Replacement for 13x21-1/2x1 Merv 11 Pleated Ultra Allergen AC Furnace Air Filter 6 Pack Similar to the 3M Filtrete Ultra Allergen 13x21-1/2x1 Air Filter Made in the U.S.A. Actual Size: 12 7/8 Inches (Length) x 21 1/2 Inches (Width) x 3/4 Inches (Thickness) Electrostatically-charged, pleated fabric filter media 3 Month Filter Life