EPS Frequently Asked Questions

What is Expandable Polystyrene (EPS)?

Expandable polystyrene or EPS beads are solid, spherical particles or beads of polystyrene containing pentane, a hydrocarbon that acts as a blowing agent. When the beads of EPS are exposed to dry, saturated steam, they expand up to 50 times their original volume, to obtain the foam material called Expanded Polystyrene widely used as acoustic and thermal insulation and as packaging.

In the market, two families of EPS can be found: Regular and Flame Retardant (FR). The FR grades contain a flame retardant additive that reduces both ignitability and flame propagation. Due to the incorporation of the flame retardant additive, the range of FR products are not approved for food contact applications and are mainly used for building and construction applications.

What are the main applications of Expandable Polystyrene (EPS)?

EPS is a thermoplastic foam material that can be used as a cost effective energy saving material for building insulation or as an efficient, durable material for packaging.

Roughly speaking, 70% of the EPS volume sold in Europe is used in building and insulation applications and 30% in packaging.

How is Expanded Polystyrene manufactured?

The expanded polystyrene foam is manufactured, starting from expandable polystyrene beads, in a three stage process:

1) Pre-expansion (or prefoaming) stage:
During this stage, the Expandable Polystyrene is expanded with dry saturated steam to form prefoam using a batch or a continuous pre-expander:

Batch pre-expander:
Batch-expanders are closed, pressurized vessels. Thus the temperature inside the chamber can be above 100°C as the operating pressure can be above atmospheric pressure. This can allow low densities to be achieved in one step. They operate using batch additions of raw material introduced at the top of the pre-expander vessel; the prefoam is discharged after the expansion step at the bottom of the vessel. The amount of raw bead, the steam pressure and the residence time of the raw beads inside the pre-expander allow control of the density of the prefoamed beads.

Continuous pre-expander:
Continuous pre-expanders are cylindrical vessels that operate at atmospheric pressure, thus the temperature of the chamber is limited to 100°C. The raw material is introduced continuously at the bottom of the vessel by a screw feed and the pre-expanded beads leave the machine through an overflow chute that is adjustable in height. Steam is introduced continuously at the bottom of the vessel. The screw feed rate, steam pressure and the height of the overflow chute allow control of the density of the prefoamed beads.

As the temperature inside the vessel increases with the introduction of the steam, to between 90 and 100°C, the polystyrene softens and the vapor pressure of the pentane increases. These two processes cause the beads to expand by up to 50 times their original volume and the formation of the foam structure of closed cells within the beads. This cell structure contributes to the excellent insulation and mechanical properties of this foam material.

2) Maturing stage:
After the pre-expansion stage, the steam and the blowing agent condense within the cell structure of the prefoam creating a partial vacuum in the cells of the pre-expanded beads. Therefore, the prefoamed beads are not resilient: after a deformation, the spherical shape is not recovered. During the maturing stage, the beads are stored in silos for several hours according to their density and ambient conditions to allow the permeation of air into the cells, equalizing the pressure differential and allowing physical stabilization of the prefoamed beads. During this stage, the level of residual pentane blowing agent inside the beads also decreases with the maturing time. Changes in the maturing stage (e.g. time and ambient conditions) can be a useful tool in modifying the subsequent processing characteristics of the EPS prefoam.

3) Molding stage:
The stabilized beads are introduced into a close mould and submitted to an additional steaming step. The beads undergo a further, limited secondary expansion step, filling all the space of the mould and fusing together to take the shape of the mould (block or shape molded object).

What are the recommended storage conditions for Expandable Polystyrene?

INEOS Styrenics EPS grades are normally packed in 1000 kg net semi-bulk containers, termed “Octabins”. To minimize the loss of expansion agent, each Octabin has a separate plastic film liner, tied at the neck. EPS beads should be stored in closed containers, preferably below 20°C. They should be protected from adverse weather conditions and direct sunlight where ever possible.

Processing performance deteriorates over time as storage temperature rises. The expansion agent, pentane, is flammable and can form ignitable concentrations in part-empty containers and storage hoppers. All possibility of ignition should be avoided and adequate floor-level ventilation provided in storage and processing areas. They should be protected from adverse weather conditions and direct sunlight wherever possible. Under such conditions, products delivered in Octabins can be stored for up to two months after delivery.

Are Expandable Polystyrene (EPS) grades hazardous to human health?

No, they are chemically unreactive, generally recognized as being biologically inert, and not classified as hazardous to human health. Please refer to the relevant Material Safety Data Sheet for further information.

What are the environmental benefits of EPS?

Ozone depleting substances are not used in the manufacture of EPS.
EPS reduces the greenhouse effect by improving insulation standards and helping to minimize CO2 emissions.

Expanded polystyrene consists of approximately 98 % air and 2% polystyrene by volume. The low density of expanded polystyrene allows packaging weight and transport costs to be reduced.

EPS is a stable and inert material which retains its original properties and insulation performance, allowing energy savings over its lifetime. EPS can be recycled, incinerated or disposed of in landfill without detriment to the environment. The high calorific value of EPS will assist the combustion of municipal solid waste. In landfill sites, EPS does not degrade to produce voids, and does not emit dangerous gases or contribute to groundwater pollution.

Can Expandable Polystyrene (EPS) grades be used for food packaging?

Yes. This is demonstrated, for instance, by its huge demand in food packaging applications, where they are approved for food contact and provide the highest levels of sanitation, insulation and protection. (includes solid polystyrene as well!)

Can Expandable Polystyrene (EPS) be attacked by moisture?

EPS is virtually insensitive to moisture, and will absorb almost no water even when immersed for long periods. This means that moisture has virtually no effect on EPS insulating products after installation, and the original insulation value of EPS is therefore guaranteed for a long time.

For further information on INEOS Styrenics EPS grades and their use, please contact your local INEOS Styrenics representative.