<P> A cooler, portable ice chest, ice box, cool box, chilly bin (in New Zealand), or' esky' (Australia) most commonly is an insulated box used to keep food or drink cool . Ice cubes are most commonly placed in it to help the things inside stay cool . Ice packs are sometimes used, as they either contain the melting water inside, or have a gel sealed inside that stays cold longer than plain ice (absorbing heat as it changes phase). </P> <P> The portable ice chest was invented by Richard C. Laramy of Joliet, Illinois . On February 24, 1951, Laramy filed an application with the United States Patent Office for a portable ice chest (Serial No . 212,573). The patent (#2,663,157) was issued December 22, 1953 . </P> <P> The Coleman Company popularized the cooler with its initial offering of a galvanized cooler in 1954 . Three years later, Coleman developed a process to make a plastic liner for coolers and jugs . </P> <P> Coolers are often taken on picnics, and on vacation or holiday . Where summers are hot, they may also be used just for getting cold groceries home from the store, such as keeping ice cream from melting in a hot automobile . Even without adding ice, this can be helpful, particularly if the trip home will be lengthy . Some coolers have built - in cupholders in the lid . </P>

What kind of plastic are coolers made from