The food bags in the market can be used to hold dry, wet, raw and cooked food, which is safe and nontoxic. The plastic bags used to pack food in food factories and preserves factories are of course nontoxic. The plastic bags used to pack daily commodities, clothes, shoes and socks, electrical appliances and hardware parts may be toxic, so it is not suitable to hold food. Non-toxic plastic bags are generally made of polyethylene, while toxic plastic bags are made of polyethylene. This is a compound that will be toxic to human body. Besides, in the process of processing PVC resin into plastic bags, some auxiliary materials such as plasticizers, stabilizers, pigments, etc. are added, and some auxiliary materials are toxic. These toxic substances are easily extracted by oil or water in food and eaten with food, which is harmful to human health. PVC resin itself is non-toxic. If PVC resin is produced, Reducing the free vinyl chloride monomer to a very small amount, and strictly selecting non-toxic auxiliary materials when making the finished product, you can make non-toxic PVC plastic bags. Generally, it is difficult to distinguish polyethylene plastic bags from PVC plastic bags. By burning, it can be easily identified. Polyethylene can burn, the flame is blue, the upper end is yellow, and it emits paraffin smell when burning. PVC is extremely difficult to burn. When it is on fire, it is yellow, the outside is green, and it gives off a pungent smell of hydrochloric acid. Whether plastic bags are toxic in use is also related to the use method. Some food bags are printed with words such as trademarks. If they are turned over during use, it is unsafe to let the food be stained with these pigments.