Air Defense HD 20x25x4Air Defense Mechanical MERV 8A has tested to have longevity and strong media with an efficient design to its construction. From the pleat consistency, durability, and the comparison to other high capacity MERV 8 filters, the Air Defense Mechanical MERV 8A stands alone as the new standard. ***Actual Size*** 19 1 2" x 24 1 2" x 3 5 8" MEDIA 100% synthetic, proprietary media resists moisture and damage Mechanical efficiency achieves MERV 8A rating before