In the gentle heat of a sauna, wood is more than a surface — it’s an atmosphere, a scent, a grounding presence. And not just any wood will do. At UK Hardwoods, our reverence for the natural beauty and integrity of British-grown timber has led us to embrace thermally modified wood — or thermo wood — as the ideal material for sauna cladding and interiors.
What is Thermo Wood?
Thermo wood is timber that has been carefully heat-treated at high temperatures (usually between 160–220°C) in a controlled, oxygen-free environment. This natural process alters the structure of the wood without the use of chemicals, enhancing its durability, stability, and resistance to moisture, decay, and insects.
For saunas, where heat and humidity are constant, these properties make thermo wood a standout choice.
Why Choose Thermo Wood for Saunas?
Superior Stability
Thermally modified timber is far less prone to movement than untreated wood. In sauna environments, where fluctuations in temperature and humidity are extreme, this means reduced risk of warping, shrinking, or swelling — and a finish that endures beautifully.Toxin-Free and Eco-Friendly
The process uses only heat and steam, making thermo wood a safe, chemical-free solution — essential in wellness environments where air purity matters. And when sourced responsibly, it carries a small environmental footprint.Rich, Deep Colour
One of the most striking features of thermo wood is its rich, smoky hue — a natural outcome of the heat treatment. It lends a sophisticated, spa-like atmosphere to sauna interiors and deepens the wood’s natural grain patterns.Soft Touch, Safe Heat
Thermally modified ash and other species we work with retain a fine, smooth surface that is gentle to the touch — even when hot. It doesn’t splinter easily and remains comfortable under bare skin, making it ideal for benches and panelling alike.Longevity
Thermo wood offers remarkable resistance to decay, even in high-moisture environments. With proper installation and ventilation, your sauna timber will remain a source of warmth and calm for many years.
British-Grown Timber ......
We craft our thermo wood from British ash — a species celebrated for its strength and expressive grain. Thermally modifying it transforms ash into a resilient, dark-toned material that performs exceptionally well in saunas while maintaining a beautiful connection to its natural origin.
Grown in Britain certified and traceable back to its woodland source, our thermo ash brings sustainability and story into every steam-filled moment.
Would you like to use British-grown thermo wood in your sauna project?
We’d be delighted to help. Whether you’re a homeowner, architect or designer, we offer bespoke solutions in locally grown, thermally modified timber — crafted to bring warmth, wellness and beauty to modern spaces. Find out more here about our Thermally Modified Ash options.
