The chemical composition and physical and chemical properties of different foods are different, so the protective requirements of different foods for food packaging bags are also different. For example, the cake is rich in oil, soft, and has a certain * water content requirement, so * at least should meet the following requirements: oil-proof high oxygen barrier (to prevent oil leakage and grease oxidation), high moisture resistance (prevent The cake loses moisture and becomes hard and hard). For example, the packaging of tea should be high oxygen barrier (to prevent the active ingredients from being oxidized), high moisture resistance (tea leaves moisture and mildew), high light resistance (the chlorophyll in tea leaves will change due to sunlight), high resistance aroma Sex (tea molecular aroma components are easy to disperse, but lose the taste of tea. In addition, tea is also very easy to absorb external odor), and a considerable part of the current market tea is ordinary PE, PP and other transparent plastic bags, greatly wasting tea effective Ingredients, the quality of the tea is not guaranteed. Contrary to the above-mentioned foods, fruit, vegetables and the like have a respiration option after picking, that is, the package is required to have different transmittances for different gases. For example, after the roasted coffee beans are packaged, the carbon dioxide is slowly released. The cheese also produces carbon dioxide after packaging, so they should be packaged with high oxygen barrier and high carbon dioxide permeability. The packaging of fruits and vegetables is often required to be mildew-proof, because the small mist on the inner wall of the bag will cause a series of unfavorable biochemical use of fruits and vegetables, resulting in easy browning and perishable fruits and vegetables. Different varieties of fruits and vegetables and the same kind of fruits and vegetables of different maturity have different requirements on the ventilation and selectivity of packaging materials. The protective requirements for packaging of raw meat, processed meat, beverages, small foods, and baked goods are also very different. For example, the coating of canned meat should be resistant to sulfur, the coating of canned fruit should be acid-resistant, the container of the inflated beverage should be able to withstand certain pressure, and the packaging container of alcohol should be resistant to alcohol and block the aroma. Therefore, the packaging should be scientifically designed according to the different nature of the food itself and the protective requirements of the water.