If one of the hydrogen atoms on every ethylene monomer in polyethylene is replaced by a chlorine atom (note that this is not how this material is actually made!), you get PVC, or polyvinylchloride. It’s the third-largest-volume polymer produced each year behind polyethylene and polypropylene. It is a very tough polymer, so it is used to make pipes and flooring among many other things. PVC can also be softened (technical term: plasticized) by introducing small organic molecules, like phthalates (a benzene ring with two esters). Among other applications, plasticized PVC is used to insulate electric wires and to make your garden hose.