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What is polystyrene?
Polystyrene is an industrial plastic material used in a wide range of different applications such as protective packaging, cushioning fragile items, manufacturing office items, etc... Expanded polystyrene (EPS) is used as thermal insulator. Expanded polystyrene is produced when styrene monomers interconnect introducing simultaneously hydrocarbons such as pentane.  The resulted polymer appears as beads whose diameters vary from 0.2 to 0.3 mm.  This takes place in a petro-chemical factory. Going from expandable polystyrene to expanded polystyrene is realised on production sites of manufacturers in 3 successive stages.

Pre expansion:
Inside a Stainless Steel tank and with water steam, polystyrene granules are expanded by free exposure to steam to form larger beads whose volume can be up to 30 times the volume of the raw beads prior to expansion. These pre-expandable beads have thus a honeycomb core made of 98% of air.

The stabilization or maturing stage:
Then these pre-expandable beads (prepuff) are usually fed to holding bins for several hours to stabilize.

Moulding:
Pre-expandable beads finally put in a closed mould are again in contact with water. They expand again (up to 50 times their previous volume). During moulding, the steam causes fusion of each bead to its neighbours, thus forming a homogeneous product. Since it is made out of 98% of air EPS is greatly used in the packaging industry in order to protect the products all along the logistic chain up to the end user consumer.