Express bag has the characteristics of low cost, easy to use and good waterproof performance. Express bags are mainly used in the express industry to transport all kinds of goods, materials and other packaging. In addition to express companies, many online shopping industries, such as vipshop and jumeiyoupin, will customize their own special express bags in order to enhance their image and promote their brands. Nowadays, there are two kinds of commonly used materials for express bags: one is low-density polyethylene (LDPE), which is what we often call PE; the other is high-density polyethylene (HDPE), which is what we often call Po. The difference between PE and Po express bags is that PE printing color is brighter, transparency is better and softer; PO is relatively brittle and has good mechanical properties. The main material of our domestic express bag is PE, while the foreign one is PE and PO composite.