If one of the hydrogen atoms on every ethylene monomer in polyethylene is replaced by a benzene ring (note again that this is not how this material is actually made!), you get PS, or polystyrene. Polystyrene is usually the fourth-largest-volume polymer produced globally, with billions of pounds made annually. Polystyrene can be manufactured into parts (like CD cases, furniture, and eating utensils), or air can be mixed with the polymer to make a foam used in insulation both for your house and your coffee cup. Styrofoam® is a trademarked name held by the Dow Chemical Company for foamed polystyrene.