Cedar vs Thermowood Sauna: Which Timber Should You Choose?

Cedar vs Thermowood Sauna: Which Timber Should You Choose?

Table of Contents

What Is Thermowood?

Thermowood is timber that has been thermally modified — heated to temperatures of 180–230°C in the absence of oxygen. This process permanently alters the molecular structure of the wood without the use of any chemical treatments. The thermal modification process:

  • Degrades and rearranges the wood's hemicellulose structure, dramatically reducing the timber's ability to absorb and release moisture
  • Reduces the equilibrium moisture content by 40–50% compared to untreated timber
  • Produces a chemically stable, dimensionally stable material that resists swelling, shrinking, and warping
  • Creates a uniformly dark brown colouration throughout the timber (not just a surface treatment)

Thermowood is most commonly produced from Scandinavian pine or spruce, treated according to the ThermoWood® standard developed in Finland. In Australia, it is typically imported from Scandinavia and distributed nationally.

What Is Western Red Cedar?

Western Red Cedar (Thuja plicata) is a North American softwood species renowned for its exceptional natural durability, stability, and moisture resistance. Unlike thermowood — which is artificially enhanced — cedar's properties are entirely natural.

Key natural properties of western red cedar:

  • Contains natural oils (primarily thujaplicin and thujic acid) that resist moisture, rot, and insect attack without any treatment
  • Extremely low density (420–450 kg/m³) making it one of the lightest structural timbers
  • Natural dimensional stability — cedar has one of the lowest shrinkage rates of any commercially available timber
  • Distinctive reddish-brown colouration with pleasant natural aromatic properties
  • Naturally resistant to ultraviolet degradation better than most softwoods

Head-to-Head Comparison

Property Western Red Cedar Thermowood
Natural vs treated 100% natural Thermally modified (no chemicals)
Colour Reddish-brown; weathers to silver-grey Dark chocolate brown throughout
Moisture resistance Excellent (natural oils) Very good (modified structure)
Dimensional stability Very good Excellent (superior to cedar)
Natural fragrance Yes — pleasant cedar aroma Minimal (aroma largely removed by process)
Weight Very light (420–450 kg/m³) Lighter than untreated; similar to cedar
UV resistance Good Good (may require similar maintenance)
Surface hardness Soft (easy to dent) Harder than untreated; similar to cedar
Typical cost (Australia) Higher (imported from North America) Moderate (imported from Scandinavia)
Sustainability Variable (depends on certification) More sustainable (less timber volume needed for same performance)

Appearance and Aesthetics

Western Red Cedar: Has the classic warm reddish-brown appearance immediately after installation, with a pleasant natural grain variation. If oiled regularly, it maintains this colour. If left untreated outdoors, it gradually weathers to an elegant silver-grey — a popular look in Scandinavian-inspired outdoor spaces. The natural colour variation and grain character give cedar installations a premium, organic aesthetic.

Thermowood: Has a distinctive, uniform dark chocolate brown appearance. This colouration is consistent throughout the timber (not just the surface), meaning cuts and machined edges have the same colour as the face. The darker aesthetic has a contemporary, almost architectural quality that suits modern home designs well. Thermowood also weathers with UV exposure — turning silver-grey similar to cedar if not oiled, and maintaining the dark tone with regular oiling.

Durability in Australian Conditions

Australia's climate — intense UV, variable humidity, extreme temperature cycling in some regions — puts outdoor timber under significant stress. Both cedar and thermowood perform well in Australian conditions relative to untreated softwoods, but with different strengths:

Cedar in Australia: The natural oils in cedar provide good protection against the main Australian climate risks: moisture, UV, and biological attack. In tropical regions (high humidity, rainfall), cedar's natural oil content gives excellent biological resistance. In arid climates (extreme temperature cycling, intense UV), cedar's natural dimensional stability reduces cracking. Requires oiling every 12–18 months to maintain appearance and extend lifespan.

Thermowood in Australia: The thermal modification process provides excellent dimensional stability in the humidity cycling characteristic of most Australian climates — thermowood is less likely to gap, split, or warp with seasonal humidity changes than cedar. However, the thermal modification does not enhance biological resistance as significantly as cedar's natural oils — in persistently wet conditions, thermowood may require more attention than cedar to prevent surface mould. Requires oiling on a similar schedule to cedar.

Thermal Performance

For sauna applications, both timbers behave similarly in high-temperature, high-humidity conditions. The relevant properties are:

  • Low thermal conductivity: Both cedar and thermowood have low thermal conductivity — they don't become uncomfortably hot to the touch in the sauna interior
  • Dimensional stability at temperature: Both handle the repeated thermal cycling of sauna use well, with thermowood slightly superior in dimensional stability
  • Steam resistance: Both are suitable for steam (löyly) environments; cedar's natural oils provide a slight advantage in very high humidity applications

For interior sauna bench timber, aspen is often preferred over both cedar and thermowood due to its lower thermal conductivity and essentially zero resin content. See our Traditional Sauna Buyers Guide for complete interior material guidance.

Maintenance Requirements

Both cedar and thermowood require periodic oiling to maintain their appearance and extend service life:

  • Western Red Cedar: Annual oiling with a UV-protective exterior timber oil (Organoil, Cutek, Feast Watson Deck Oil) is recommended for most Australian climates. Oil is applied to clean, dry timber with a brush or cloth. 1–2 coats per application.
  • Thermowood: Similar annual oiling requirement. Thermowood accepts oil well but tends to absorb it more readily than cedar — slightly more oil per coat is sometimes required.

Band tension (for barrel saunas) should be checked annually for both timber types — thermal cycling over Australian seasons can cause slight compression changes in the barrel stave structure.

Environmental and Sustainability

Both western red cedar and thermowood can be sourced from sustainably managed forests, though certification varies by supplier:

  • Western Red Cedar: Look for FSC (Forest Stewardship Council) certified cedar from British Columbia, Canada. Some cedar is harvested from old-growth forests — avoid this and seek plantation-grown or secondary forest sources.
  • Thermowood: Produced from Scandinavian pine and spruce — species grown in sustainably managed Nordic forests with strong regulatory oversight. The thermal modification process uses no chemical biocides, reducing environmental impact. FSC-certified thermowood is available.

From a sustainability perspective, thermowood has an advantage in requiring no chemical treatment for durability enhancement. However, both are responsible choices when sourced from certified sustainable forestry.

Cost Comparison

Pricing varies by supplier and specification, but general trends for Australian market:

Application Western Red Cedar (AUD/m²) Thermowood (AUD/m²)
Sauna cladding/exterior $120–$200/m² $90–$150/m²
Sauna kit (barrel sauna) Typically $1,000–$3,000 premium over thermowood Reference price

Cedar saunas typically command a price premium of 15–30% over comparable thermowood saunas, reflecting both the higher material cost and the prestige associated with the cedar brand in premium sauna construction. See full pricing: Sauna Cost Guide Australia.

Our Verdict

Both cedar and thermowood are excellent choices for Australian sauna construction. The right choice depends on your priorities:

Choose Western Red Cedar if:

  • The natural fragrance of cedar is important to you (a genuine sensory element of the sauna experience)
  • You prefer the warmer, more natural reddish-brown aesthetic
  • You're in a persistently wet climate and want maximum biological resistance
  • Premium aesthetics and the "cedar brand" are part of your wellness investment

Choose Thermowood if:

  • Superior dimensional stability (less warping, gapping) is your priority
  • You prefer the contemporary dark-chocolate aesthetic
  • You're in a climate with significant humidity cycling and want minimal maintenance
  • Value for money relative to performance is your primary consideration

For more guidance on sauna types and construction: Barrel Sauna Buyers Guide Australia | Outdoor Sauna Buyers Guide Australia

This article is for informational purposes only.

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