The 16" X 25" X 1" Series 400 Standard Capacity Pleated Air Filter Utilizes State-of-the-Art 100% Synthetic Media to Achieve Exceptionally High Levels of Efficiency with the Lowest Resistance to Air Flow Available. The Series 400 Filter is Extremely Effective in Removing Many Airborne Irritants such as Pollens, Molds, Dander, and Dust