Thermowood: The Ultimate Accessory for Your Sauna
A sauna is built around one simple idea: heat, handled well. Every surface you touch, lean against or sit on needs to remain comfortable through intense heat, repeated temperature changes and regular exposure to moisture. That makes the choice of timber more important than it might seem.
This is where Thermowood comes into its own. Thermally modified timber combines stability, comfort and a naturally rich appearance, making it particularly well suited to sauna interiors where the material is experienced as much through touch as through sight.
What Is Thermowood?
Thermowood is timber that has been thermally modified in a controlled process using heat and steam, typically at temperatures between 160°C and 215°C depending on the treatment level and species. No preservatives or chemical additives are required for the modification itself. Instead, heat alters the wood's cellular structure, reducing its ability to absorb moisture and improving its dimensional stability. The result is timber with a deeper colour, reduced moisture movement and greater resistance to biological deterioration than untreated wood. And in a sauna, those changes matter.
Comfort Comes First
Think about the parts of a sauna you interact with most: the bench beneath you, the backrest behind you and the walls around you. Thermally modified timber is well suited to these touch surfaces because many commonly used Thermowood species have relatively low thermal conductivity. They do not become uncomfortably hot as quickly as denser materials, helping create a more comfortable seating and resting experience.
Some untreated softwoods can release resins when exposed to high temperatures. In a sauna, where timber is in direct contact with skin, even a small amount can become an unpleasant surprise. Thermal modification significantly reduces resin-related issues, leaving behind a cleaner, more comfortable surface.
Made for Heat, Humidity and Change
A sauna rarely stays at one temperature. It heats up, moisture enters the room, water meets hot sauna stones, and eventually everything cools down again. Repeating this cycle can cause untreated timber to absorb and release moisture, leading to dimensional movement over time.
Thermowood absorbs less moisture and therefore moves less. That improved stability helps boards remain flatter, joints stay more consistent and wall and ceiling cladding retain their intended appearance through repeated cycles of heating and cooling. Its reduced moisture uptake also contributes to improved resistance to decay and fungal deterioration, an important consideration in an environment where heat and humidity regularly meet.
The Colour Becomes Part of the Experience
One of Thermowood's most distinctive qualities is its colour. Thermal modification naturally deepens the appearance of timber, producing tones that can range from warm honey and amber to richer brown shades, depending on the species and treatment. Unlike a surface coating, this colour is created through the modification of the timber itself. The result is particularly effective in a sauna. Under warm, subdued lighting, the deeper timber tones create an interior that feels calm and enveloping, while the natural grain keeps the space connected to the material itself. Thermally modified Ayous is one example; naturally pale and fine-grained, it takes on a warmer, more consistent character after thermal modification while retaining the understated appearance that makes it suitable for interiors.
Less Maintenance, More Material
A sauna should feel like a place to switch off, not another surface that demands constant attention. Thermowood requires relatively little maintenance when properly specified and installed. Regular cleaning and adequate ventilation help keep the timber in good condition, while its improved dimensional stability reduces some of the movement associated with untreated wood. Because the thermal modification process itself does not rely on preservative impregnation, there is also no need to introduce a conventional chemical preservative treatment simply to achieve the modified properties.
Where Can You Use Thermowood in a Sauna?
Thermowood can be considered across several parts of a sauna interior:
Benches and backrests - where touch, comfort and stability are essential
Wall and ceiling cladding - for a continuous, warm timber surface
Door frames and trims - where heat and moisture resistance are important
Outdoor sauna cabins - where the timber also needs to respond to changing weather conditions
The right species, profile and treatment level will depend on the specific application.
A Material That Knows Its Limits
Thermal modification improves dimensional stability and durability, but it can also reduce some mechanical properties of timber. That is why Thermowood should be specified according to its intended use rather than treated as a universal structural material. Benches, cladding, backrests and trim are very different applications from load-bearing construction. The right species and grade, paired with proper detailing and installation, are what allow the material to perform at its best.
Bring Thermowood Into Your Sauna With Saraswati Wood
Choosing the right timber is the first step to a sauna that feels as good as it looks, and Saraswati Wood can help you get it right. Our Thermowood range includes Thermo Pine, Thermo Ash, Thermo Ayous and Thermo Oak, offering a choice of grain, tone and character for benches, backrests, wall and ceiling cladding and trims. If you are planning an outdoor sauna cabin, the same range gives you options that can respond to changing weather conditions.
Whether you are an architect specifying a wellness space, a designer working on a private spa or a homeowner building a sauna of your own, our team can help you match the species and profile to your application. Explore the Saraswati Wood Thermowood collection, or get in touch with us to discuss your project and request a quote.
