Synthetic polymers are made up of long chains of atoms, arranged in repeating units, often much longer than those found in nature. It is the length of these chains and the patterns in which they are arrayed that make polymers strong, lightweight, and flexible. In other words, it's what makes them so plastic.

Most plastics are made from chemicals that come from petroleum (oil), natural gas, or coal. Heating these chemicals causes them to break down into molecules. (Molecules are groups of two or more atoms, which are the tiny building blocks of everything.) Scientists then join these molecules into chains.

Plastics are polymers. A polymer is a substance made of many repeating units. The word polymer comes from two Greek words: poly, meaning many, and meros, meaning parts or units. A polymer can be thought of as a chain in which each link is the “mer,” or monomer (single unit).

Plastic is defined as a material that contains an essential ingredient an organic substance of large molecular weight. It is also defined as polymers of long carbon chains. Carbon atoms are linked in chains and are produced in long-chain molecules.