Tier1 Replacement for 18x18x1 Merv 11 Pleated Ultra Allergen AC Furnace Air Filter 6 Pack Similar to the 3M Filtrete Ultra Allergen 18x18x1 Air Filter Made in the U.S.A. Actual Size: 17 3/4 Inches (Length) x 17 3/4 Inches (Width) x 3/4 Inches (Thickness) Electrostatically-charged, pleated fabric filter media 3 Month Filter Life