Plastics consist of long chains of molecules called polymers. These chains are made of repeating patterns of smaller molecules. Each of the smaller molecules forms a "link" in the polymer's chain. In some plastics, the chains are rigid and are lined up like logs flowing down a river. In others, they are flexible and tangled like spaghetti on a plate. These different structures give plastics their most notable characteristic, the ability to be shaped. In fact, the word plastics comes from the Greek word plastikos, which means able to be shaped.