Knauf XTherm Sol Th31: a new essential EPS insulation for under-screed insulation

A national launch after a year of conclusive regional tests

Following a pilot phase of tests conducted in the South of France, Knauf is launching Knauf XTherm Sol Th31 nationwide. Featuring an optimized and versatile formula, Knauf XTherm Sol Th31 has widely established itself, among various types of installation companies, as the new alternative for floor insulation.

For a year, they were able to assess its wide range of performance and applications, particularly for under-screed insulation and "under sealing mortar", a technique particularly widespread in the South of France.

Knauf XTherm Sol Th31: performance under screeds and slabs that makes EPS the preferred choice for specifiers

Knauf XTherm Sol Th31 panels are available in 1200 x 1000 mm formats, with thicknesses from 20 to 200 mm in 10 mm increments; a specific feature of EPS allowing for optimized implementation, as close as possible to the project requirements.

Compliant with standard NF EN 13163, Knauf XTherm Sol Th31 offers certified thermo-acoustic performance, up to a thermal resistance (R) of 6,45 m².K/W. It also boasts optimized environmental data compared to conventional under-screed solutions, primarily regarding the global warming index, with only 9,59 kg CO₂²/m² for example, for the 100 mm thickness. All thicknesses in the XTherm Sol Th31 range have a clearly identified value in Environmental Product Declarations (EPDs), designed according to the NF EN 15804+A2 standard, a single reference based on INIES from 1^er January 2026.

Finally, EPS is appealing because of the possibility of recycling clean offcuts with the Knauf Circular take-back program.^®In both construction and demolition, particularly when polyethylene vapor barriers are used before laying slabs and screeds, Knauf XTherm Sol Th31 offers a good thickness-to-thermal resistance ratio. With its grey EPS (expanded polystyrene) of λ 0.031 W/(mK), it also stands out for its reduced thickness compared to a white EPS panel of equivalent thermal resistance. Furthermore, the thermal resistance of 3,20 m².K/W, a common requirement for these types of applications, is achieved at a thickness of just 100 mm. Finally, in terms of acoustic insulation, especially in multi-family housing, Knauf XTherm Sol Th31 proves to be a compliant solution, providing up to 22 dB of impact noise reduction (at a thickness of 200 mm), as evidenced by supporting documentation.

Knauf XTherm Sol Th31: great versatility at the service of all professionals

This innovative Knauf XTherm Sol Th31 offers a multitude of possible applications and is perfectly suited for creating glued, floating or sealed floor coverings. It can therefore be installed under screed (according to standard NF DTU 52.10), under hydraulic slab (according to standard NF DTU 26.2), under sealing mortar (NF DTU 52.1), or even under low temperature underfloor heating/cooling or electric radiant heating (NF DTU 65.14 and CPT 3606_V3) and under reinforced concrete slab on grade (NF DTU 13.3).

Guaranteeing simplified implementation, Knauf XTherm Sol Th31 will appeal to the entire chain of building professionals. Indeed, its great versatility will be an asset for distributors who will be able to meet a maximum number of applications with a universal solution.

In terms of installation, masons, screeders, and general contractors will certainly appreciate its ease of installation in one or two layers. Indeed, Knauf XTherm Sol Th31 comes in panels with straight edges, unlike the tongue-and-groove panels found in most underlayment solutions. These straight edges mean simplified installation with no specific orientation to follow. Furthermore, with Knauf XTherm Sol Th31, a maximum number of offcuts can be reused on-site, or even on other projects if they are not intended for recycling. Added to this is the ease of cutting the EPS (for example, with a hot wire cutter), which is particularly appealing to screeders. Finally, other advantages include quick and precise cutting, good panel end-to-end connection, and the guarantee of continuous insulation without thermal bridging.

Feedback from the company Mattout, specializing in tiling in Marseille

Testimony of Charlie Bremond, site manager at Mattout, involved in the renovation of the RockyPop hotel in Marseille where 70 m² Knauf XTherm Sol Th31 under-screed insulation was installed with a 2-layer installation of 100 mm thickness (i.e. 200 mm in total).

• Total thermal resistance: 6,45 m².K / W
• Project management: Alpine Engineering & Consulting (74)
• Client: SAS HCM (74)

“Our company has been working on floor, wall, and facade coverings in the Bouches-du-Rhône region for nearly 30 years. We installed Knauf XTherm Sol Th31 because it met both the thermal and acoustic requirements of the project management team. As an installation company, we particularly appreciate working with expanded polystyrene panels with straight edges because, in addition to their recyclability through Knauf Circular, they offer excellent value.”^®There are far fewer losses or falls on the construction site. Charlie Bremond, site manager at Mattout