Thermo wood

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Thermally modified wood — also known as thermo wood — is natural solid timber that has been enhanced through a high-temperature treatment process without the use of chemical additives.

All these terms refer to the same technology: altering the internal structure of wood exclusively through heat and steam.

Today, thermo wood is widely used for sauna and steam room interiors, humid environments, as well as for cladding and bench construction.

The treatment process consists of several stages:

1. Deep Drying

The wood is dried to a very low moisture content.

2. Thermal Treatment at 150–220 °C

During this phase:

• Natural wood sugars break down 

• Hygroscopicity (moisture absorption) is reduced 

• The fiber structure changes

3. Stabilization

The material is gradually cooled, stabilizing its new geometry.

This is why thermally modified wood demonstrates improved dimensional stability and increased resistance to moisture.

Thermo wood is especially valued in sauna environments, where materials are constantly exposed to high heat and humidity.

Key properties include:

✔ Reduced moisture absorption 

✔ Enhanced dimensional stability 

✔ Resistance to biological influences 

✔ Comfortable thermal conductivity 

✔ A uniform, rich tone

These characteristics make thermo aspen, thermo alder, and thermo linden popular choices for steam rooms.

Thermally modified wood is widely used for:

• Sauna and steam room cladding 

• Wall and ceiling panels 

• Interior finishing elements 

• Exterior façade applications

Thanks to its stable geometry, thermo boards maintain clean seams and consistent form even under temperature fluctuations.

Sauna benches experience the highest level of stress. Thermo wood is valued for bench construction because of:

• Stability when heated 

• Reduced moisture absorption 

• Comfortable surface temperature 

• Long-term color consistency

This is why thermo aspen, thermo alder, and thermo linden are frequently selected for sauna benches and loungers.

Traditional aspen, linden, and alder have been used in sauna construction for decades and remain reliable, time-tested materials.

Thermal modification does not replace natural wood — it expands its performance potential.

Natural Wood:

• Maintains a light, natural tone 

• Creates a classic sauna atmosphere 

• Performs well with proper installation and ventilation

Thermo Wood:

• Offers a deeper, richer color 

• Provides enhanced dimensional stability 

• Is less sensitive to humidity fluctuations

The choice depends on operating conditions and the desired design concept.

Thermally modified wood is applied in:

• Sauna and steam room interiors 

• Cladding and bench construction 

• Shower areas and spa zones 

• Residential interior finishes 

• Facades, terraces, and pergolas

Thermal treatment always gives wood a darker, more expressive tone. Untreated natural wood retains its light, natural color and classic appearance. Therefore, the choice is always a balance between technical requirements and design vision.