Tier1 Replacement for 16x25x4 Merv 11 Ultra Allergen AC Furnace Air Filter 6 Pack Captures 90% of harmful airborne particles such as dus, pollen, pet dander, mold spores, smog, & more Similar to the 3M Filtrete Ultra Allergen filter Actual Size: 15 1/2 inches (length) x 23 1/2 inches (width) x 3 3/4 inches (thickness) 100% synthetic material offers significantly higher particulate efficiency Recommend filter life of 3 months to reduce damage to your furnace / ac unit