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Types of Foam Insulation for EWI

Foam insulation is a highly versatile material with a wide range of applications. Due to its excellent thermal capabilities, polystyrene is commonly used in EWI (external wall insulation) systems to improve the thermal performance of houses.  

In today’s post, we’re going to be laying out the facts and comparing the three types of foam insulation that are commonly used for EWI – EPS, XPS and PIR!

Expanded Polystyrene Insulation (EPS)

  • EPS (expanded polystyrene) is a rigid and tough, closed-cell foam insulation which is manufactured by the expansion process. It is usually white or grey (known as graphite EPS) and is made of pre-expanded polystyrene beads.
  • It is arguably the most versatile of all rigid foam insulation boards because it can be used in Roof, Wall, Floor, Below Grade and Structural applications such as EWI (external wall insulation) and pipe insulation.
  • 98% air because it is not very dense. The air pockets in the insulation board are what makes it great insulation.
  • Lightweight so reduces fuel consumption when being transported.
  • Can be recycled.
  • Low pollution manufacturing process because steam and water are the key ingredients for producing EPS, the water is reused many times so there is no waste.
  • Maintains thermal conductivity for the length of its life.
  • Inert and innocuous – it does not biodegrade and leach chemicals into landfill water systems or gases into the air that might contribute to global warming

Extruded Polystyrene Insulation (XPS)

  • XPS (extruded polystyrene) is closed-cell rigid foam insulation, manufactured by the extrusion process. The plastic resin is liquefied, then extruded through a die to form a closed-cell material that uses trapped air as its insulating medium.
  • XPS has a high compressive strength due to the density of the foam and is therefore suitable for use in wall, floor and roof applications.
  • It is often used in wetter environments as it is more waterproof than EPS due to its closed-cell structure.
  • Won’t support mould and mildew growth – a highly hygienic foam insulating material as it also won’t release toxins.
  • Long-term, stable thermal conductivity, so its performance will not degrade over time.
  • Can be successfully recycled where facilities exist.

Polyisocyanurate Insulation (PIR)

  • PIR (polyisocyanurate) is an insulation board that offers a high level of thermal protection for your home.
  • PIR is made of closed-cell rigid foam with injected gas.
  • The foam board is then sandwiched with materials such as fibreglass, aluminium foil or other organic materials.
  • Can be used on flat and pitched roofs, floors, walls and cavity insulation.
  • The types of PIR boards that you can get include: foil-faced PIR boards; Cavity PIR boards; Mineral-coated, glass-faced or bonded to plywood PIR boards and finally floor, walls and roof insulation boards.   
  • Releases nontoxic gas which can reduce the thermal conductivity over time, thereby meaning it may need replacing and reinstalling.
  • In some cases, has shown signs of delaminating.

Thermal Performance of Foam Insulation

Insulation material: Thermal performance:
EPS 0.032W/(m2K)
XPS 0.034W/(m2K)
PIR 0.023W/M2K

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