☆ Irish-based sauna specialist ☆ Founder-led · 15 years project experience ☆ Personal advice & local support
☆ Irish-based sauna specialist ☆ Founder-led · 15 years project experience ☆ Personal advice & local support
Spruce has long been one of the most popular choices in sauna construction – and for good reason. With its bright, inviting appearance and excellent insulating properties, it creates a pleasant, natural indoor climate. Sourced from sustainably managed European forests, spruce is a regional, eco-friendly material that’s easy to work with and ideal for the interior of saunas.
Spruce can also be used in outdoor applications, provided it receives regular care. To maintain its beauty and structural integrity over time, we recommend applying protective treatments such as oils or weatherproof stains. For those willing to invest a bit in maintenance, spruce offers an authentic, high-quality wood at a very attractive price.
Thermowood is made from the same high-quality, regional spruce – but enhanced through a chemical-free heat treatment process. This thermal modification changes the wood’s cellular structure, making it highly resistant to moisture, dimensionally stable, and suitable for outdoor use without the need for chemical preservatives.
Especially in Ireland’s humid and changeable climate, Thermowood offers clear advantages for outdoor saunas. It’s exceptionally durable, low-maintenance, and naturally weathers to an elegant silvery-grey tone over time – no ongoing treatments required.
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More Information| Property | Spruce | Thermowood |
| Density | ~430 kg/m³ | ~470 kg/m³ |
| Moisture resistance | Moderate | High |
| Maintenance | Regular oiling | Minimal |
| Colour | Light beige | Deep brown |
| Durability class (EN 350) | Class 4 | Class 2–3 |
Both spruce and thermowood are sourced from sustainably managed Nordic forests. Thermowood’s heat-treatment process is completely chemical-free, using only heat and steam, making both materials safe and environmentally friendly options for your sauna.
Spruce is an untreated softwood. It naturally absorbs moisture and reacts more strongly to Ireland’s changing weather conditions. To keep its surface protected, regular oiling or staining is necessary. This prevents moisture penetration, reduces UV damage and helps maintain the wood’s appearance over time.
Thermowood, on the other hand, is heat-treated at approximately 180–215°C. This permanently alters the wood structure, making it far less hygroscopic and significantly more dimensionally stable. As a result, thermowood requires much less maintenance. Occasional oiling is optional if you want to preserve its deep brown colour, but even without treatment it weathers evenly and remains structurally durable.
The durability class (EN 350) is an EU standard that describes how resistant a wood type is to biological decay such as fungi and rot.
In general, the lower the class number, the more naturally durable the wood is.
Either way, both materials provide the quality, warmth and authenticity that define true European sauna craftsmanship.
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