It is well known that expansion by heat and contraction by cold is the basic physical property of almost all substances.

However, a few substances violate this law under certain conditions. For example, when the water temperature drops below zero, the volume not only does not shrink but increases, part of the polymer material after special technology (process) treatment, has the performance of thermal shrinkage. The products that take the thermal shrinkage property of some polymer materials as the main function of the product or use the thermal shrinkage property to realize the main function of the product are thermal shrinkage products (or thermal shrinkage products).

Industry concept: Thermal shrinkage material, also known as polymer shape memory material, is a kind of intelligent material that combines polymer material and radiation processing technology. Ordinary high polymer materials such as polyethylene, polyvinyl chloride, etc. are usually linear structure, after the radiation effect of the electron accelerator and other radioactive sources into a network structure, these materials will have a unique "memory effect", expansion, cooling finalize the frame of the material. When being heated these changed materials can shrunk to the original shape.

Irradiation is a key link to ensure the quality of thermal shrinkage products. At present, electron accelerator under beam irradiation is the main irradiation method for thermal shrinkage materials and the core of product modification. The development of thermal shrinkage materials must be accompanied by the development of irradiation technology and irradiation equipment.