XPS and EPS insulation: the difference is in the details



Whether or not a building complies with today’s increasingly stringent energy standards greatly depends on the type of insulation used. XPS and EPS are two popular insulation materials, each with their specific qualities. This article provides an overview of the differences between both materials, enabling you to select the best type of insulation material for your project.

What is XPS insulation

XPS (Extruded Polystyrene insulation) is manufactured using a process of extrusion. This continuous process results in a closed cell structure with a smooth skin on the top and bottom of the board. XPS’ closed cell structure prevents water penetrating the structure of the insulation board and provides long term strength and durability.

Because of the way XPS boards are manufactured they offer the following benefits:

  • Extremely moisture-resistant and particularly suitable for inverted roofs, thanks to its closed cell structure.
  • Exceptional compressive strength and therefore often used under slabs, concrete floors, foundations and underground works, etc.
  • Low thermal conductivity which guarantees a high thermal insulation performance
  • Lightweight, easy to cut and install.
  • 100% recyclable.

SOPREMA offer a wide array of EFYOS XPS insulation boards which can be integrated into your roofing and waterproofing systems.

How does EPS insulation differ to XPS?

EPS (Expanded Polystyrene insulation), also known as Styrofoam, is manufactured using beads of foam within a mould. Heat or steam is applied directly to the beads which causes them to expand and fuse together. One cubic meter of EPS contains about 10 million beads, each counting approximately 3,000 cells which are closed off and filled with air. EPS is, in other words, composed of 2% polystyrene and 98% air. The manufacturing process results in a closed cell structure, but not a closed cell insulation board (due to voids that can occur between the beads).

EPS is lightweight and easy to process. Because it is made of only one material, EPS is also easy to recycle.

XPS versus EPS insulation

XPS and EPS have some key differences:

  1. Thermal conductivity: both XPS and EPS provide good thermal conductivity performance. However, the air trapped in the voids in the EPS will conduct heat. A much higher density EPS board will be required to match the thermal performance of XPS insulation.
  1. Compressive strength: in general XPS has a greater compressive strength than EPS. For EPS to achieve the same compressive strength as XPS, the density of the foam would need to be increased, often resulting in a greater thickness of board being required.
  1. Water vapour diffusion resistance: EPS has a water vapour diffusion resistance of 30-70, whereas XPS reaches 80-250. Slightly more permeable to air and moisture, EPS is less resistant to water vapour than XPS. If you’re looking to insulate a space prone to humidity (e.g. floors, cellars and foundation walls), XPS is your best option.

Do you have any questions about SOPREMA’s innovative insulation solutions? Don’t hesitate to contact us!