Polymers are chemical compounds made up of molecules linked in long, repeating chains. Plastics are a particular type of polymer, consisting of long chains of these molecules. While all plastics are polymers, not all polymers are plastics, meaning plastic is a subset of polymers. Polymers consist of uniform molecules created from smaller monomers, whereas plastics are long-chain molecules made from larger monomers. Polymers can be either natural or synthetic, but plastics are always synthetic material.