What is expanded polystyrene (EPS) exactly?

By: Tamara Middleton, Sales Representative – Architectural Products

EPS (Expanded Polystyrene) is a closed cell insulation manufactured by expanding a polystyrene polymer.  Originally discovered in Germany by Edward Simon by accident. Polystyrene is extracted from crude oil along with many other products.  4% of crude oil is used for plastics and 0.1% of the plastics is used for polystyrene. The production process uses a pure hydrocarbon, which does not contain halogens and does not damage the ozone layer.


Polystyrene’s main component is styrene (C8H8), derived from petroleum and formed by a reaction between ethylene (C2H4) and benzene (C6H6).  The styrene is polymerized by heat and beads are formed by suspension.  These tiny beads are expanded using special blowing agents, to achieve the right density.  This pre-expansion involves heating the beads with steam or hot air.  The pre-expanded beads are then aged for 24 hours, allowing the air to diffuse into the beads, cooling and drying them.  Once aged, the beads are molded, using low-pressure steam, expanding them again and fusing them.

While waste or used EPS can be incinerated creating only carbon dioxide and water if done correctly, it is usually recycled.  Recycled EPS can be used in many office products, hangers, CD cases, and even crown molding.  According to the EPS Industry Alliance, 125 million pounds of EPS were recycled in 2013, with a commercial recycling rate of 34 percent.


  • The Balance, ‘Introduction to EPS Recycling’ by Rick LeBlanc, October 20, 2015
  • About.com, ‘What is EPS – Expanded Polystyrene’ by Todd Johnson
  • Made How, ‘Expanded Polystyrene Foam (EPF)
  • Jayshree Machines & Tools, ‘What is EXPANDED POLYSTYRENE (EPS)’
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