Can IXPE/EPE foam (Isolon / Warmlex) be used under underfloor heating systems and infrared film?

Short answer: Yes, IXPE/EPE foams such as Isolon and Warmlex can be used under certain electric and water-based underfloor heating systems, provided you choose the correct foil-faced or non-foil type and follow the heating manufacturer’s installation guidelines.

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This article is for EU installers, distributors and designers who use underfloor heating and want to know when IXPE/EPE foam (Isolon, Warmlex and similar materials) is suitable as an insulation or reflective layer beneath the system.

When is IXPE/EPE foam suitable under underfloor heating?

In many underfloor heating systems polyethylene foam is used as a thin insulation and decoupling layer. Typical examples include:

• Infrared (IR) heating film – where a thin foil-faced foam is placed directly under the film to reflect heat towards the room and provide a smooth base.
• Electric cable or mat systems – where denser IXPE/XPE foam can be used as a supplementary insulation layer under screed or dry boards.
• Warm water (hydronic) systems – where foam is used as part of the floor build-up, usually together with other thermal insulation materials.

The key is to match the foam type and thickness with the heating system design and temperature limits specified by the manufacturer.

Which foam types are typically used?

For Isolon, Warmlex and related products the most common options under heating systems are:

• Foil-faced IXPE/XPE foam (Isolon) – used under infrared film and some electric systems as a reflective layer that sends radiant heat upwards. The foil surface must remain electrically insulated from live parts.
• Non-foil IXPE/XPE foam – used where a thin, thermally stable foam is required under screed, boards or heating pipes, without direct contact between foil and heating elements.
• NPE foam (Warmlex) – suitable in low-temperature systems or as part of a multi-layer build-up where operating temperatures are moderate and load-bearing requirements are limited.

In all cases the foam must withstand the expected surface temperature of the floor and the mechanical loads in the construction.

— check the maximum operating temperature of the heating system and choose a foam grade that fits this range;
— use foil-faced foam only where an electrically insulated reflective layer is allowed by the system design;
— avoid direct metal-to-metal contact between foil surfaces and live heating elements;
— if in doubt, send your floor build-up to LIRIDA-M and the heating supplier for review before installation.

Frequently asked questions

• What thickness of foam do you recommend under underfloor heating? In many projects 2–5 mm foam is used as a thin insulation and decoupling layer. Thicker layers may be used only if allowed by the heating system design and load calculations for the floor.
• Can I rely on Isolon or Warmlex as the only thermal insulation in the floor? Usually no. IXPE/EPE foams are excellent as a thin reflective or additional layer, but they do not replace the main structural insulation defined in the building design.