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Wood Types: Spruce vs Thermowood

Choose your type of wood

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.

  • Bright, natural look
  • Good thermal insulation
  • Sustainably sourced and regional
  • Excellent value for money
  • Ideal for sauna interiors
  • Requires regular maintenance
  • Protective coating recommended for exposed areas
  • Contains natural resin

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.

  • Perfect for outdoor use
  • Highly weather-resistant and long-lasting
  • Low maintenance and stable in shape
  • Resin-free – ideal for high temperatures
  • Sustainably made from regional spruce
  • Elegant, naturally darker appearance
  • Slightly higher initial cost
  • Naturally darker colour tone (will gradually grey)
A rectangular wooden plank with visible grain and knots is centred over a blurred background of an outdoor sauna interior, featuring wooden benches, a towel, and a water ladle.A rectangular wooden plank is centred against the background of a sauna room with wooden benches, a towel, a ladle, a sauna hat on the left, and hints of an inviting outdoor sauna just beyond the scene.
"Spruce is light and fresh, while Thermowood is heat‑treated for extra strength and durability."

Technical Comparison

PropertySpruceThermowood
Density~430 kg/m³~470 kg/m³
Moisture resistanceModerateHigh
MaintenanceRegular oilingMinimal
ColourLight beigeDeep brown
Suitable forIndoor and sheltered outdoor useFull outdoor exposure
Durability class (EN 350)Class 4Class 2–3

 

Sustainability

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.

 

Which Wood Should You Choose?

  • Choose Spruce if you prefer a light, traditional look and do not mind occasional maintenance.
  • Choose Thermowood if your sauna will be fully exposed to the elements or if you want the lowest-maintenance option.

Either way, both materials provide the quality, warmth, and authenticity that define true European sauna craftsmanship.