What determines the strength of a plastic bag?

Plastic bags are made from a ubiquitous polymeric material called polyethylene. This starts with ethylene, usually extracted from natural gas, which is then processed into a polymer, forming long chains of carbon and hydrogen atoms. These chains can vary depending on the type of polyethylene used, but they all contribute to the manufacture of various types of plastic bags.

 

Materials used to make plastic bags

Low Density Polyethylene Plastics

LDPE plastic is made from low-density, branched polymeric materials. Rather than remaining linear, these polyethylene chains unfold in many different combinations of lines. This produces a very light, almost film-like plastic used to make the tearable bags dry cleaners use to wrap cleaned clothes.

 

High Density Polyethylene Plastics

HDPE stands for high density polyethylene and is the most common type of polyethylene used to make shopping bags. This plastic consists of straight molecular chains with few molecular chains that remain linear from end to end. This linear structure creates a very strong material, which is why the average grocery bag is light but can withstand many times its own weight without tearing.