The polystyrene thus produced is one of the thermoplastic materials sometimes called linear polymers. These are materials that soften on the applications of heat and harden as they cool.
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The expanded foam (known as EPS) is produced as small beads containing a pentane blowing agent which is expanded by treatment with steam to form pre-foam of the required density. The pre-foam is then fed into moulds and more heat (steam) is applied. This heat fuses the beads together to produce items in a variety of shapes and sizes or to make blocks for cutting into sheets and other products.