EPS (expanded polystyrene): definition and uses

What is EPS?

EPS, or expanded polystyrene, is a rigid thermal insulator made of polystyrene beads expanded with steam and then fused together. The resulting material consists mostly of trapped air, which accounts for its insulating properties and light weight.

In floor insulation, it is used in two forms that differ in both application and purpose.

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Panels or granules: two different approaches

The panels are cut and laid edge-to-edge on a pre-leveled surface. They are suitable for new, even slabs without exposed utility lines. Every cut made around a pipe creates a joint that must be carefully sealed.

The insulating mortar based on EPS granules changes the game entirely. The beads are mixed with a binder and then poured like a lightweight screed. The material conforms to the substrate, flows around pipes, fills voids, and levels out.

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Why insulating mortar is relevant for renovation

Old floors are rarely level and are often crisscrossed by utility lines added over the years. This creates two simultaneous challenges: insulating and leveling.

Insulating mortar solves both in a single operation. Where you would otherwise need a leveling compound followed by insulation, a single layer acts as a filler, a leveling agent, and an insulator. For height differences of several centimeters, it is also less expensive than spraying PUR throughout this thickness.

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Performance and thickness

The thermal conductivity of EPS is higher than that of polyurethane, which means that more thickness is required to achieve the same performance. In an insulating mortar, the presence of the binder further degrades this value slightly compared to a pure board.

This is only a problem when height is limited. When there is volume to fill, the additional thickness is no longer a constraint but an advantage: it is necessary anyway to reach the correct level.

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Compressive strength, a criterion to check

An insulating layer under a screed must be load-bearing. EPS that is not dense enough will compress under loads and cause the floating screed to flex, which leads to cracks.

The compressive strength stated by the manufacturer must therefore be compatible with the intended use of the room. A living room and a warehouse do not have the same requirements. Both solutions, PUR and EPS, are described on our thermal insulationpage.