Plastics are a category of materials otherwise known as polymers, which are made of long chains of molecules, meaning that they’re pliable and easily shaped. These polymers exist in nature — for instance, cellulose, the material that makes up the cell walls of plants, is a common polymer. It’s only over the last 200 years that we’ve learned how to make polymers synthetically to produce a cheap, strong, lightweight, and flexible material: plastic.