Plastics are organic polymeric materials (those consisting of giant organic molecules) that are plastic—that is, they can be formed into desired shapes through extrusion, moulding, casting, or spinning. The molecules can be either natural—including cellulose, wax, and natural rubber—or synthetic—including polyethene and nylon. The starting materials are resins in the form of pellets, powders, or solutions; from these are formed the finished plastics.

Polyethylene is probably the polymer you see most in daily life. Polyethylene is the most popular plastic in the world. It is a polymer of ethylene. (a gaseous unsaturated hydrocarbon. It is the simplest alkene) This is the polymer that makes grocery bags, shampoo bottles, children's toys, and even bullet proof vests. For such a versatile material, it has a very simple structure. A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom. We can simply draw it like this, only with the chain of carbon atoms being many thousands of atoms long:

Sometimes it's a little more complicated. Sometimes some of the carbons, instead of having hydrogens attached to them, will have long chains of polyethylene attached to them. This is called branched, or low-density polyethylene, or LDPE. When there is no branching, it is called linear polyethylene, or HDPE. Linear polyethylene is much stronger than branched polyethylene, but branched polyethylene is cheaper and easier to make.

Although the raw material for polyethylene comes from coal, a non-renewable resource, polyethylene is environmentally friendly since polyethylene products are durable and recyclable. As well, polyethylene film is used in Tetra Brik cartons which reduce waste. The development of polyethylene has often been credited with initiating the modern plastics industry. Many newer plastics such as polypropylene, polystyrene, and Teflon, are variations of polyethylene. However, the reliability, relative cheapness, and versatility of polyethylene ensure its continued use in the future. While both LDPE and HDPE are white, translucent, waxy textured thermoplastics with excellent resistance to water, chemicals, and electricity, HDPE is much more rigid and resistant to heat and surfactants. These qualities of HDPE make it useful for shampoo, detergent, and bleach bottles.