Expanded Polystyrene


Literally translated, polystyrene is "polymerised styrene". The expandable form (known as EPS) is initially produced as small beads containing a blowing agent. The beads expand when treated with steam, forming a lightweight "prefoam" of the required density.
These prefoamed beads are then processed in a mould to form large blocks that are then cut into sheets or other shapes. Alternatively, for high volume products, the beads are moulded into their final product form in individual moulds.

Typical Applications

Cold storage insulation: floors, walls, ceilings. Lagging: pipes, tanks, vessels, valves and ductwork insulation. Industrial and domestic insulation: floors, walls, ceilings and roofs. Building and construction: concrete fill and for expansion joints. Insulated panels and door manufacture: core insulating material. Packaging: for maintaining the temperature of perishables or the protection of fragile goods.


Chemical Resistance

Resistant to: brine, fresh water, weak mineral acids, strong mineral acids (except concentrated nitric), weak alkalis, strong alkalis, most vegetable oils. Non-resistant to: mineral oils, chlorinated hydrocarbons, petrol, benzine, esters and ketones.

Burning Characteristics

EPS is a combustible material. The amount of heat liberated by EPS undergoing combustion is very small and if this is dissipated then sustained ignition is unlikely. The 'FR' grades are treated with a fire retardant which causes the material to shrink away from a source of ignition without burning if exposed for a short period, but burns if kept in contact with the flame for a longer period.

Flame Retardant Grade (FR)

Flame retardant polystyrene (FR Grade) is available in all densities. Surface fire index results according to SABS 0177, part III yield the following results:
Spread of flame index 4,4. Heat contribution index 0,9. Smoke emission index 9,9. Surface fire index 4,7. Class 5.

Material Properties of EPS


Unit EPS 15 EPS 20 EPS 30
Density kg/m3 15 20 30
K value Thermal conductivity W/m.K 0,040 0,038 0,036
Water-Vapour Diffusion Resistance Value - 20 30 60
Compression strength at 10% deformation kPa 60 100 165
Short term compression strength kPa 80 120 210
Long term compression strength kPa 20 30 50
Shear strength kPa 190 270 460
Tensile strength kPa 200 280 440
Water absorption fully-submerged after 7 days % volume 1,7 0,6 0,5
Water absorption fully-submerged after 1 year % volume 5,0 4,0 3,0
Linear expansion co-efficient M/m 7.10-5 7.10-5 7.10-5
Co-efficient of friction 0,5 0,5 0,5
Heat capacity J/kg K 1500 1500 1500
Temperature range °C -110/+70 -110/+70 -110/+70
Limited exposure maximum temperature °C +110 +110 +110
Youngs modulus kPa 4000 6000 10000

See also Healthy Building with EPS