Specification
Why Thermally Modified Aspen Is the Best Interior Wood for a Sauna
An expert guide to sauna interior wood — why thermally modified aspen is the optimal choice, and why Wellness One uses it as standard across the entire range.
By Wellness One Lifestyle · Published 2026-08-02 · Updated 2026-08-02
Interior Wood in Outdoor Saunas
The interior wood of a sauna is in contact with extreme heat, humidity, and the human body. The choice of interior wood directly affects comfort, hygiene, durability, and the quality of the sauna experience.
Why Aspen?
Aspen is the preferred interior wood for premium saunas for several reasons:
Non-resinous — Aspen does not contain resin. At high temperatures, resinous woods (such as pine and spruce) release sticky, aromatic compounds that can cause skin irritation and leave residue on benches and walls.
Dimensionally stable — Aspen is less prone to warping, cracking, and shrinkage than other softwoods. This is important in the extreme temperature and humidity cycles of a sauna.
Low thermal conductivity — Aspen has a lower thermal conductivity than many other woods, meaning the bench surface remains comfortable to touch even at 110°C.
Light colour — The pale, clean appearance of aspen creates a bright, welcoming sauna interior.
Why Thermally Modified?
Thermal modification takes aspen's natural properties and enhances them significantly. The process:
- Increases dimensional stability — reduces moisture absorption and movement
- Improves resistance to mould and bacteria
- Eliminates any residual resin
- Produces a consistent, uniform appearance
Wellness One uses thermally modified aspen that has been oiled for additional protection. This is the highest specification interior wood available for outdoor saunas.
What to Avoid
Untreated softwood (pine, spruce) is the most common interior wood in budget saunas. It is resinous, prone to warping, and requires regular treatment. Hardwoods (such as oak) are too dense and retain heat on the surface, making them uncomfortable to sit on.
Frequently Asked Questions
What is the best wood for a sauna interior?
Thermally modified aspen is the optimal choice for a sauna interior. It is non-resinous, dimensionally stable, resistant to moisture and bacteria, and comfortable to touch even at high temperatures. Wellness One uses thermally modified aspen as standard.
Why is aspen used in saunas?
Aspen is naturally non-resinous — it does not release sticky sap at high temperatures. It is also light in colour, dimensionally stable, and has a low thermal conductivity, making it comfortable to sit on even at 110°C.