Heat shrinkable casing is made of high quality high polymer, the ratio of science, mechanical blending polymer, after molding, products by the electron accelerator radiation crosslinking, continuous expansion, product soft, flame retardant, shrinking fast, widely used in connectors, household appliances, solder joint protection, wire end, wiring signs, lighting, office equipment, electrical equipment, communication equipment, resistor products such as insulation protection and metal corrosion, antirust processing, and antenna protection