What is the difference between XPS and EPS Insulation?


The energy efficiency of a building often depends on the materials that create its envelope. Selecting the appropriate insulation type is crucial in delivering the required insulation performance for your project. The use of XPS and EPS insulation in building construction offers great flexibility, compatibility and thermal efficiency for all areas of the building envelope system. But what is the difference between EPS and XPS insulation? 


Extruded polystyrene insulation (XPS) 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. The closed cell structure of extruded polystyrene (XPS) prevents water penetration to the structure of the insulation board and provides long term strength and durability.

Expanded Polystyrene insulation (EPS) is manufactured using beads of foam within a mould, heat or steam is then applied directly to the beads which causes them to expand and fuse together. This process produces a  closed cell structure, not a closed cell insulation board, due to voids that can occur between the beads.

Compressive strength 

Compressive strength is demanded in the most challenging environments such as under slabs on a flat roof, concrete floors, foundations, plaza and podium decks and cold storage. In general, when comparing EPS and XPS board densities, the compressive strength of XPS is greater than that of 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.

Thermal conductivity

Insulation is one of the most practical and cost effective ways to improve a building’s energy efficiency, by improving the insulation in new and existing buildings, significant cost savings and reductions in energy usage can be achieved. 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.

EFYOS XPS insulation, is an industry leading range of extremely high performance, extruded polystyrene (XPS) closed cell insulation boards, suitable for many demanding and varied insulation applications including inverted and green roofs including zero fall roof designs in conjunction with SOPREMA zero fall waterproofing systems, floors, walls and below ground works.


Water vapour diffusion

Water vapour diffusion resistance (μ) of EPS ranges from approximately 30 – 70  compared to the water vapour diffusion resistance (μ) of XPS that ranges from approximately 80 – 250. XPS is often selected over EPS for wetter environments that require a higher water vapour diffusion resistance value. 

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The information contained within this article is generic and not based upon one single manufacturer’s  production process. To find out more please contact a waterproofing and insulation expert at SOPREMA UK.