first, plastic is collected and taken to a recycling center, where it is "sorted out". when plastic is sorted out, symbols have to be printed on every recyclable plastic product used. there are two types of plastic: "polyethylene" and "polymer". there are two kinds of polyethylene plastic, too: "high density polyethylene" (hdpe), and "low density polyethylene" (ldpe). hdpe plastic is usually used to make furniture, and ldpe plastic are usually things like milk jugs, plastic and grocery bags.