The main raw materials of ordinary plastic bags are high-pressure polyethylene and biaxially oriented polypropylene. Polyethylene and polypropylene are mainly used to make films, containers, pipes, monofilaments, wires and cables, daily necessities and so on. It can be used as high-frequency insulating material for TV, automobile, radar, etc. Direct contact with food is toxic. At present, the convenient bag for soft-packed food adopts a convex-concave seal in the bag, and a seal is formed in the bag, so that after the sealing edge of the bag is torn, the convex-concave seal acts as a bottle cap and can be opened and closed freely. Its advantages are: 1, easy to carry, can be repeatedly opened and sealed, convenient to eat, and keep the original color and flavor of food. 2. Wide application range, suitable for vacuum packaged foods such as fruits and vegetables, candied milk powder, meat, poultry, aquatic products, condiments, etc. 3. It can replace metal cans, glass bottles and plastic bottles to package food, each with its own advantages. At the same time, compared with them, it saves raw materials, has light weight and low cost; Small size, warehouse saving and convenient storage and transportation; Cooking sterilization has the advantages of fast heat transfer, less loss of food nutrients, low energy consumption and high efficiency; Destruction saves trouble, does not hurt people, etc. Convenient food bags with flexible packaging are widely used, convenient to use, low in price, strong in practicability, good in social and economic benefits, and have high development and popularization value and broad market prospects.