Duramold is a composite material process developed by Virginius E. Clark. Birch plies are impregnated with phenolic resin, such as Haskelite and laminated together in a mold under heat (280 °F, 138 °C) and pressure for use as a lightweight structural material. Similar to plywood, Duramold and other lightweight composite materials were considered critical during periods of material shortage in World War II, replacing scarce materials like aluminum alloys and steel.