Polystyrene (6)

Polystyrene is typically (but not always) a homopolymer i.e. that it is composed only of the monomer styrene in combination with itself[1]. It can be classified as either a thermo plastic material (can be heated to its melting point, cooled, and re-heated again without significant degradation) or a thermoset material (which instead of burning liquefies, allowing it to be easily injection moulded and then subsequently recycled, although thermoset plastics will not reliquify once they are "set" in solid form; they can also only be heated once, (the first heating usually during injection moulding process), this causes the thermoset materials to set resulting in a chemical change which cannot be reversed)[1].

The foam form of polystyrene (EPS) is most often used as a packaging material particulalry in high value items such as televisions, washing machines, dishwashers etc [1] where it has been moulded to fit the product it is protecting. Polystyrene beads are tiny bits of expanded polystyrene and are commonly found in bean bags and childrens toys such as in stuffed animals/teddy bears and as home insulation. The larger loose form of EPS (in the shape of 'figures of 8') are most commonly used to protect smaller less expansive items although their use is being phased out with more environmentally friendly alternatives (such as brown paper packaging) which can be re-used and recycled more easily. XPS is a higher density foam typically used in applications such as architectural building models[1].