Austech External Building Products examines the difference between expanded (EPS) and extruded polystyrene (XPS).

There is a great deal of confusion with many people assuming they are essentially the same; however, expanded and extruded polystyrene are very different products beginning with the manufacturing process.

Expanded Polystyrene (EPS) is made using small expandable beads that inflate with heat, and are placed into a mould, where they expand to fit the shape. The expanded beads trap air, which gives expanded polystyrene its insulation properties, but also leaves it vulnerable to water absorption, reducing the insulation’s effectiveness over time.

Extruded Polystyrene (XPS) is made by mixing polystyrene pellets with chemicals that liquefy the pellets, following which a blowing agent is injected into the mixture, forming billions of miniature air pockets. This frothing mixture is then pushed through a shaping die to give the required size and minimise wastage. Once cooled, the boards can be further shaped and wastage returned into the manufacturing process.

Foamular extruded polystyrene is manufactured by Owens Corning Asia Pacific employing an in-house patented Hydrovac technology that makes the blowing agent more efficient and helps guarantee long term retention of R-values. A member of EPA Climate Leaders Program, Owens Corning is committed to reducing greenhouse gas emissions in the manufacturing process through product performance.

Extruded polystyrene’s unique production process gives it superior R-value in comparison to expanded polystyrene and many other building materials, helping reduce temperature fluctuations and improve energy efficiency for the entire product lifecycle.

R-values of some common building materials:

  • Foamular metric XPS 250/50mm = R1.78
  • Expanded polystyrene 50mm, m grade = R1.20
  • Brickwork, 110mm = R0.18
  • Weather boards, 12mm avg, pine = R0.08
  • Fibre cement sheet, 6mm = R0.019
  • Concrete slab, 2400kg/m³, 100mm = R0.069
  • Plaster board, 10mm = R0.059

Foamular extruded polystyrene’s closed cell structure prevents water absorption unlike expanded polystyrene, which does not have a closed cell structure and easily absorbs water, dramatically reducing its thermal properties and overall structural integrity. Water absorption is a leading cause of loss in R-value in various insulation products.

Foamular extruded polystyrene also has a high compressive strength allowing its use in high pressure applications, such as under slab insulation and in PRMA roofing applications. This structural rigidity also improves the product’s lifecycle: for instance, when Foamular is used as a render substrate, its improved impact resistance and structural strength help reduce future damage and cracks to the render.

Extruded polystyrene from Owens Corning, therefore, outperforms expanded polystyrene (EPS) in the three key areas of R-value, moisture resistance and compressive strength, making Foamular a more efficient and durable insulation product.

Image: Home with Foamular substrate