let's study together, just found it.

according to the pressure during polymerization, polyethylene plastics can be divided into high pressure polyethylene or low density polyethylene (LDPE) and low pressure polyethylene or high density polyethylene (HDPE). High pressure polyethylene is mainly used to make food plastic bags, plastic wrap, etc. Low-pressure polyethylene is mainly used to make food plastic containers, pipes, chopping boards, etc. Polypropylene plastic film can be stretched longitudinally and transversely to change its mechanical properties and increase its strength and transparency. According to the stretching direction, polypropylene plastic film is mainly used to manufacture food plastic bags, especially composite plastic bags. Polypropylene can also be processed into food containers that are both resistant to low temperature and high temperature, such as fresh-keeping boxes and containers for microwave ovens. ?

comparison: high-pressure low-density polyethylene is softer than low-pressure high-density polyethylene!