Polystyrene has a number of properties: it has a low melting point, it is translucent before tint is added, and it is hard and brittle. Depending on the application it is used for, Polystyrene's properties will change. It is rigid, but when heated to 100 Celsius, it becomes a flowing liquid.
The material can also be put into a foamed state. This is often seen when the foam is dried and then used for packing peanuts. Polystyrene is slow to break down or biodegrade, making it a candidate for recycling, but also a focus of controversy in the environmental sectors. Most of polystyrene's properties are influenced by short-range attractions, called van der Waals, between the polymer chains. These chains consist of thousands of hydrocarbon atoms, making the attractive force very high. When the material is heated, the chains become flexible and elastic.
The heating and molding of the plastic is often used in extrusion or injection molding machines. The hard plastic is fed into a hopper, which then falls into either a die or a screw. The dies and screws are heated and the plastic is melted, allowing it to be pressed into the mold or through the die and into the required shape. Once cool, the plastic holds it shape and becomes very durable.