Rubber air bag, also known as concrete prefabricated hollow plate rubber inflatable core mold, bridge inflatable core film, rubber inner mold, is a kind of internal mold of different shapes that can expand and contract by vulcanizing rubber polymer characteristics and high strength fiber cloth. It is mainly used in the casting and forming engineering of the concrete beam of highway bridge. It is also used in culvert drainage projects. After the rubber air bag is filled with compressed air, the air bag stretches and expands to meet the design requirements of its cross-section, and the inflation pressure is determined according to the manufacturer's logo. It is easy to use, economic and durable, can be used repeatedly for nearly a hundred times, soft contraction when not inflated, arbitrary folding, curling, inflation after expansion has enough strength to withstand the pressure of concrete. It can replace the original wooden mold, bamboo mold and steel mold, and can be reused many times. It is a kind of concrete products supporting products to reduce costs and speed up construction progress.