Insulation ~ Extruded Polystyrene

Extruded Polystyrene (XPS) is made by mixing polystyrene and a blowing agent under pressure and then forcing the resultant fluid through a die. As it emerges from the die the fluid expands into a foam, which is shaped before it cools. Extruded is stronger than expanded polystyrene and as such is better suited applications where some load bearing is required such as below ground (for example, in providing an insulation layer in a floor).



  • Manufactured from petrochemicals so not sustainable and toxic when burnt.
  • High embodied energy.
  • Moisture tolerant and relatively durable.
  • Versatile, strong and relatively easy to fit.

Typically has a thermal conductivity or K value in the range of 0.028 – 0.036 W/m.K. (Watts per meter Kelvin ~ lower value is a better result)

Depending on thickness costs should around £7 a square metre with more specialist flooring products up to £15 a square metre.