How is EPS made

EPS is produced in a three stage process:

Pre-expansion
Tiny beads of polystyrene raw material containing an expansion agent (usually a hydrocarbon such as pentane) are expanded using steam.  The combination of heat and rapid release of the gas leads to the beads expanding to between 40 to 50 times their original volume.

Conditioning
After expansion the beads undergo a maturing phase of between 12-48 hours to enable equilibrium temperature and pressure to be reached. 

Moulding
The beads are then placed within a mould and again reheated with steam where they expand further, completely fill the mould cavity and fuse together. The moulding process can either be used to form large block or custom shapes.  When moulded, nearly all the volume of the EPS (~98%) is air.