Sheets used for blister packaging are called hard films.. Commonly used are PET (polyethylene terephthalate) hard films, PVC (polyvinyl chloride) hard films. PS hard film has low density, poor toughness, and is easy to burn. Styrene gas (belonging to harmful gas) will be generated during burning, so it is generally used to produce plastic trays for various industries. PVC hard film has moderate toughness and is not easy to burn. Chlorine gas will be generated during combustion, which will have a certain impact on the environment. PVC is easy to heat seal. It can be sealed with a sealing machine and a high-frequency machine. PET hard film has good toughness, high transparency, is easy to burn, and does not produce harmful gasses during combustion. It is an environmentally friendly material, but the price is high. It is suitable for high-end plastic products. Blister shells in European and American countries generally require PET hard film. It is not easy to heat seal, which brings great difficulties to packaging. In order to solve this problem, people compound a layer of PVC film on the surface of PET, named PETG hard film, but the price is higher.