The raw material for food bags is polyethylene, which is commonly used in high density polyethylene (HDPE), granular, and the price is about 10,500 yuan/ton. Of course, some use not only polyethylene, but also other additives, such as filling masterbatch, etc.
Plastic bags are divided into two kinds of relationships
I. Food grade
①维护食品 应具备维护食品所需的各项技术性能，如相应的 透气性、 透湿性、化学稳定性、物理机械性能、密封性(用密封实验仪测定)、遮光性、保香性等。
(1) Maintenance of food should possess all kinds of technical properties needed to maintain food, such as the corresponding permeability, moisture permeability, chemical stability, physical and mechanical properties, sealing (measured by a sealed experimental instrument), shading, aroma preservation and so on.
②消费工艺的顺应性 能顺应包装机械化和自动化消费工艺的请求，如资料的 消毒灭菌、成型、充填(有时是热填充)和封缄等工序的操作性能，以保证消费效率和包装质量。
(2) Compliance performance of consumption process complies with the requirements of packaging mechanization and automatic consumption process, such as sterilization, forming, filling (sometimes hot filling) and sealing of data, in order to ensure consumption efficiency and packaging quality.
③促进销售 包装资料和容器应具有良好的销售外观和印刷装潢的顺应性， 有助于进步食品商品价值，在市场上富有吸收力和竞争才能。 ④ 卫生平安 食品包装资料关于食品不能有任何不利的影响，包括任何的气息和有害成分的污染，确保食品的卫生平安;同时，包括应使消费者有平安卫生感。
(3) Promoting the sale of packaging materials and containers should have a good sales appearance and adaptability to printing and decoration, help to improve the value of food commodities, and be able to absorb and compete in the market. (4) Health and safety food packaging materials should not have any adverse effects on food, including pollution of any odor and harmful ingredients, to ensure food hygiene and safety; at the same time, consumers should have a sense of safety and hygiene.
(5) Other long-standing problems, such as the economy of packaging, saving resources, energy and recycling of packaging waste, environmental sanitation and ecological balance.
二、PET 聚对苯二甲酸乙二醇酯 化学式-OCH2-CH2OCOC6H4CO- 英文名：polyethylene terephthalate，简称PET，为高聚合物，由对苯二甲酸乙二醇酯发作脱水缩合反响而来。对苯二甲酸乙二醇酯是由对苯二甲酸和乙二醇发作酯化反响所得。PET是乳白色或浅黄色、高度结晶的聚合物，外表平滑有光泽。在较宽的温度范围内具有的物理机械性能，长期运用温度可达120℃，电绝缘性，以至在高温高频下，其电性能仍较好，但耐电晕性较差，抗蠕变性，耐疲倦性，耐摩擦性、尺寸稳定性都很好。
2. Polyethylene terephthalate, or PET for short, is a high polymer derived from dehydration and condensation of ethylene terephthalate. Ethylene terephthalate is obtained by the reaction of esterification of terephthalic acid and ethylene glycol. PET is a milky white or light yellow, highly crystalline polymer with a smooth and lustrous appearance. It has excellent physical and mechanical properties in a wide temperature range. It can be used at 120 C for a long time and has excellent electrical insulation. Even at high temperature and high frequency, its electrical performance is still good, but it has poor corona resistance, creep resistance, fatigue resistance, friction resistance and dimensional stability.
It has good mechanical properties, impact strength is 3 to 5 times that of other films, and good flexural resistance.
(2) Oil resistance, fat resistance, dilute acid resistance, alkali resistance, and resistance to most solvents.
(3) It has excellent resistance to high and low temperature. It can be used for a long time in the temperature range of 120 ~C, 150 ~C in short term, and - 70 ~C in low temperature. And it has little influence on its mechanical properties at high and low temperatures.
(4) Low gas and steam permeability, i.e. excellent gas, water, oil and odor resistance.
_High transparency, can obstruct ultraviolet radiation, good gloss.
_Non-toxic, tasteless, hygienic and safe, can be directly used in food packaging.