The Flanders Precisionaire HD Series 11255.021020 Disposable Filter is designed for use in a variety of filtering applications. These 10" x 20'' x 2" panel filters are specifically designed for heavy workloads. The model 11255.021020 is constructed with a synthetic media of polyester fibers bonded together with fire-resistant resin and held together with a moisture-resistant chipboard box frame. Support grilles consisting of two metal retainers provide additional support and rigidity. Precisionaire HD filters are UL 900 Class 2 listed for flammability, so when clean, the filters did not flame or emit excessive sparks when tested.