What Timber Is Best For A Sauna? Cedar vs Thermo Pine

The short answer: both cedar and thermo pine are excellent sauna timbers - but they suit different builds, budgets, and priorities. This guide breaks down exactly how they compare so you can make the right call for your sauna.

Why Timber Choice Matters More Than You Think

A sauna isn't just hot, it cycles through extremes of heat, humidity, steam, and cold air every single session. The timber you line it with needs to handle all of that without warping, cracking, sweating resin, or becoming too hot to sit on comfortably.

Get it right and your sauna feels premium, performs beautifully, and lasts decades. Get it wrong and you're looking at costly repairs, unpleasant smells, or worse.... a burn from a superheated bench.

So let's look at the two most popular options in New Zealand right now: Western Red Cedar and Thermo Pine.

What Is Western Red Cedar?

Western Red Cedar (Thuja plicata) is a softwood native to the Pacific Northwest of North America. It's been used in saunas for well over a century, and for good reason.

Naturally low in density, cedar heats up quickly and doesn't store heat the way denser timbers do. That makes it comfortable to lean against and sit on even in a hot sauna. It also contains natural oils that give it a resistance to moisture, mould, and decay without any chemical treatment.

The scent is cedar's most talked about quality. That warm, woody, slightly sweet aroma it releases in the heat is genuinely pleasant, and for many people, it's part of what makes a sauna feel like a sauna.

Key characteristics of cedar:

• Natural oils provide inherent moisture resistance
• Low thermal conductivity  (stays comfortable to touch)
• Lightweight and easy to work with
• Warm colour (pale pink to reddish brown)
• Strong aromatic properties, especially when heated
• Grades vary widely  (look for clear)

What Is Thermo Pine?

Thermo Pine is standard pine (generally spruce or radiata) that's been put through a thermal modification process. Essentially baked in a high-temperature, low-oxygen chamber at around 180–215°C. No chemicals are involved, just heat and steam.

This process changes the wood at a cellular level. The sugars that would normally cause resin bleed in a hot sauna are broken down. The moisture content is permanently lowered. The result is a timber that's dimensionally stable, far less prone to warping, and much less likely to cause the sticky, sticky resin patches you sometimes get with untreated pine.

It also darkens the timber noticeably. Thermo pine typically comes out a warm caramel to dark honey colour that many people find very attractive in a sauna interior.

Key characteristics of Thermo Pine:

• Thermally modified, no chemicals, just heat treatment
• Significant reduction in resin bleed (critical for saunas)
• Improved dimensional stability compared to untreated pine
• Darker, warmer colour than natural pine
• Generally more affordable than cedar in New Zealand
• Slightly more brittle than untreated timber (requires care during installation)

Cedar vs Thermo Pine: 

Comfort and Heat Tolerance

Both timbers perform well in terms of comfort. Neither will burn you if the sauna is built and ventilated correctly. That said, cedar has a slight edge here purely because of its natural density (or lack thereof). It's one of the least dense commercial softwoods available, and less dense timber absorbs and radiates less heat back at your skin.

Thermo Pine, while denser than cedar, still performs well. The modification process actually lowers its thermal conductivity compared to untreated pine, bringing it closer to cedar in real world comfort.

For benches specifically, the surfaces you sit and lie on, both are suitable. If you're particularly sensitive to heat, cedar gives you a small margin of comfort advantage.

Moisture and Longevity

Saunas are wet environments. Steam sessions, splashed water, condensation. Your timber takes a constant battering.

Cedar's natural oils are genuinely effective here. They give it an inherent resistance to moisture absorption and the microbial growth that comes with it. A well-built cedar sauna that's properly ventilated should last a very long time without much intervention.

Thermo Pine addresses moisture differently. The thermal process dramatically reduces the wood's ability to absorb and release moisture. This is actually the main driver of warping and cracking in timber. The result is a very stable board that doesn't swell and shrink as aggressively as untreated wood. This can actually make it more dimensionally stable than cedar in certain climates.

For New Zealand conditions, which range from the humidity of Northland to the temperature swings of the South Island, both perform well. Neither needs sealing or staining in a sauna (and you shouldn't seal the interior of a sauna anyway). 

The Resin Question

If you've ever been in an older pine sauna and noticed dark, sticky patches on the walls or bench, that's resin bleed. Untreated pine contains significant amounts of resin that liquefies at sauna temperatures and seeps out of the wood.

This is a real problem. It's messy, it can mark skin and towels, and it's very difficult to clean.

Cedar doesn't have this problem. Its oils don't behave the same way at heat.

Thermo Pine largely doesn't have this problem either. The thermal process breaks down the resin compounds before installation. Some minor bleed can occur in lower quality Thermo products or in isolated knots, but a quality Thermo Pine board should be essentially resin free in normal sauna use.

This is one of the main reasons untreated pine is generally not recommended for sauna interiors, while Thermo Pine is.

Aesthetics

This is genuinely a personal call, but it's worth thinking about.

Cedar has a warmth and variation to it, the pinkish-red grain, the subtle lustre, the natural character. It can lighten over time with exposure to steam and heat, moving toward a silvery-honey tone. 

Thermo Pine tends to be more consistent in colour. That deep caramel tone is uniform across boards and stays relatively stable over time. If you want a moody, Nordic-dark sauna interior, thermo pine delivers that look very naturally.

Neither is "better"  it comes down to the aesthetic you're going for.

Cost Considerations in New Zealand

Cedar is generally the more expensive of the two partly because it's imported, and partly because demand for it is high globally.

Thermo Pine tends to be a little more cost effective in New Zealand, partly because it's often made from New Zealand grown radiata or European pine Thats imported. 

If budget is a meaningful factor in your build, Thermo Pine gives you excellent sauna grade performance at a lower material cost.

What About Other Timber Options?

For completeness, a few others come up in sauna discussions:

Aspen, very popular in Finnish saunas. Extremely low in resin, very pale colour, stays cool to touch. Less commonly available in NZ but also worth sourcing if you can find it.

Untreated Pine or Radiata generally not recommended for sauna interiors due to resin bleed. Fine for structural framing but avoid using it for lining, benches, or ceiling.

Hardwoods — generally not suitable for sauna interiors. They absorb and radiate too much heat and can become uncomfortable or even dangerous to touch.

So Which Should You Choose?

Here's a practical way to think about it:

Choose cedar if:

• You love the natural cedar scent as part of your sauna experience
• You want a traditional, warm-toned aesthetic
• Budget is less of a concern
• You're sourcing timber from a well-established supplier

Choose Thermo Pine if:

• You want a darker, Nordic-style interior finish
• You're working to a tighter budget without compromising on performance
• You want excellent dimensional stability
• You prefer a neutral scent environment in the sauna

In practice, many builders mix the two, Thermo Pine for wall lining and cedar for the bench surfaces where comfort is most important. That combination gives you excellent overall performance and keeps costs in check.

Final Thoughts

There's no wrong answer between WR Cedar and Thermo Pine - both are proven sauna timbers that will serve you well for many years if installed correctly and the sauna is properly ventilated after each use.

The most important thing is to use timber that's specifically prepared for sauna use. Whatever species you choose, avoid any treated, sealed, or painted timber inside the hot room. Your sauna needs to breathe, and so do you.

If you're planning a build and want to talk through your setup,  heater sizing, build configuration, accessories, feel free to get in touch with us at Kauri Point Sauna. We're here to help you get it right.