The structural foam developed in the 1960s is characterized by core foaming, non-foaming of the skin layer, external hard and toughness, high specific strength (strength per unit mass), low consumption, and increasingly extensive replacement of wood. Used in the construction and furniture industries. The chemical or radiation cross-linked foaming technology of polyolefins has been successful, resulting in a significant increase in the production of foamed plastics. The foamed plastic obtained by blending, filling, reinforcing and other modified plastics has better comprehensive performance and can meet the needs of various special purposes. For example, a glass fiber reinforced polyurethane foam obtained by reaction injection molding has been used as a structural component of an airplane, a car, a computer, etc., and a foam made of polybenzimidazole filled with hollow glass beads is light and resistant to high temperatures. , has been used in spacecraft.