These 3 ply panel filters are constructed using 100% polyester fibers. Each panel filter has a specific "formula" for blending different size fibers to form the relative layers. These layers are designed to capture large particles throughout the entering layer and progressively smaller particles through the remaining layers. They capture any migrating particles and prevent the discharge of particles from the filter. These filters are constructed to produce an extremely high dust holding capacity and a MERV 11 rating.