Duo-Cube filters are medium efficiency, extended surface filters constructed of 100% synthetic fibers to meet the requirements found in various air handling systems. Duo-Cubes are offered in four media types: 1 Ply, 2 Ply, 3 Ply and 4 Ply. All four are engineered to provide an excellent combination of efficiency and extended filter life cycles and are available in Standardstyle (without an internal wire frame, for use in existing cube-type baskets without modification to equipment) and in Self-Seal style (with an internal wire frame designed to fit standard holding frames without clips or fasteners, and eliminate air bypass).