Cedar, Nordic spruce, hemlock, and aspen are all solid choices for sauna interiors, each with real trade-offs around cost, smell, durability, and sensitivity. Pine, fir, pressure-treated lumber, and hardwoods like oak should be avoided entirely.
I spent a weekend last summer helping a buddy frame out his backyard sauna. We got to the interior paneling debate and spent two hours arguing about wood. He wanted cedar. I said go with hemlock. We both had good reasons, but neither of us had looked at the actual science of what happens when different woods sit at 180°F with 20% humidity for an hour.
Here is what I found after digging into the research and talking to a few builders who have been doing this for decades.
The short answer
Cedar is the most common choice for good reason. Nordic spruce is the traditional Finnish material. Hemlock is a smart alternative if you want to save money without sacrificing performance. Aspen works well for people with sensitivities. Avoid pine, fir, and pressure-treated lumber at all costs.
But the "best" depends on what matters most to you: smell, durability, cost, or health considerations.
What happens to wood in a sauna environment
Before picking a species, understand what the wood is dealing with.
A sauna cycles between dry heat (170-200°F) and moisture from steam or sweat. The wood expands and contracts repeatedly. Resins can bleed out. Some woods release volatile organic compounds (VOCs) when heated. Others absorb moisture and develop mold.
The ideal sauna wood needs to:
- Resist warping and cracking under temperature swings
- Stay cool to the touch (low thermal conductivity)
- Not release harmful compounds when heated
- Resist moisture absorption and fungal growth
- Feel comfortable against bare skin
Cedar: the gold standard for a reason
Western red cedar is the most popular sauna wood in North America. It earned that reputation.
Cedar has natural oils called thujaplicins that act as fungicides and insecticides. That is why cedar resists rot and decay without chemical treatment. The same oils give it that recognizable smell, which most people find pleasant.
The key property for sauna use is low thermal conductivity. Cedar stays cooler to the touch than most other woods at the same temperature. When you sit on a cedar bench at 180°F, it does not burn your skin. Try that with pine and you will jump up fast.
Cedar also contains minimal resin. Resin pockets in other woods can heat up and weep sticky sap onto your skin. Cedar does not do that.
The downside: Cedar is expensive. A good-grade cedar board can cost three to four times what you would pay for hemlock or spruce. It is also softer than some alternatives, meaning it dents and scratches easier.
Nordic spruce: the Finnish tradition
Finland has more saunas than cars. They know what works.
Nordic spruce (Picea abies) is the traditional wood for Finnish saunas. It grows slowly in cold climates, producing tight grain patterns that resist warping. The wood has low resin content and a light color that reflects heat rather than absorbing it.
Spruce does not have the same aromatic compounds as cedar. It has a mild, clean smell that fades quickly. Some people prefer this because the sauna smell comes from the heat and steam, not the wood itself.
The trade-off: Spruce is less rot-resistant than cedar. In a properly ventilated sauna this does not matter much, but if your sauna has moisture issues, spruce will deteriorate faster. It also dents more easily than cedar.
Hemlock: the practical choice
Hemlock is what I recommended to my buddy, and I stand by it.
Hemlock (Tsuga canadensis or Tsuga heterophylla) has a straight grain, low resin content, and good dimensional stability. It does not warp or cup as badly as many other woods when exposed to heat and moisture cycles.
The thermal conductivity is similar to cedar. It stays comfortable against skin at high temperatures. The color is pale with subtle pink or brown tones, and it takes on a warm honey color over time.
Hemlock costs about half what cedar costs. For a full sauna build, that difference can be thousands of dollars.
The catch: Hemlock has a mild, slightly acidic smell when new. It fades after a few heating cycles. Some people notice it, most do not. Hemlock is also not naturally rot-resistant, so good ventilation is non-negotiable.
Aspen: for the sensitive
Aspen is the hypoallergenic option.
This wood has no scent, no resin, and very low VOC emissions when heated. If you have chemical sensitivities or respiratory issues, aspen is the safest bet. It is also smooth to the touch and does not splinter easily.
Aspen stays cool like cedar and spruce. It has a bright white appearance that keeps the sauna feeling light and open.
The problem: Aspen is soft. Really soft. Bench seats will show wear within a year. It also absorbs moisture more than other woods, which means it needs more drying time between uses and has a higher risk of mold if ventilation is poor.
What to avoid
Pine and fir. Both are cheap and widely available. Both are terrible for saunas. They contain high amounts of resin that will bleed out when heated. You will end up with sticky sap on your skin and a strong pine smell that becomes cloying after 20 minutes. The resin can also cause skin irritation for some people.
Pressure-treated lumber. This is not even a debate. Pressure-treated wood contains chemicals like copper azole or alkaline copper quaternary. These are designed to resist rot and insects outdoors. When heated, they can release those chemicals into the air you breathe. Do not use it.
Oak and other hardwoods. Hardwoods have high thermal conductivity. They get hot and stay hot. Sitting on an oak bench at sauna temperature will burn you. Hardwoods also expand and contract significantly with temperature changes, leading to cracking.
The practical breakdown
Here is how I think about it:
- Budget matters. Hemlock gives you 90% of what cedar offers at half the price.
- You want the classic sauna smell. Spend the money on cedar.
- You want authenticity. Nordic spruce, if you can find it.
- You have chemical sensitivities or allergies. Aspen.
- You are building in a humid climate with imperfect ventilation. Cedar handles moisture best.
One more thing about wood and health
The wood you choose affects more than aesthetics and durability.
When wood heats up, it releases volatile organic compounds. Cedar releases cedrol and thujaplicins. Spruce releases pinene and limonene. These are the compounds you smell, and they are generally harmless in the concentrations found in a sauna.
But if you have asthma or chemical sensitivities, the VOC load matters. Aspen releases almost nothing. That is why many public saunas in Europe use aspen for the benches.
The research on this is thin. A 2017 study in the Journal of Wood Science found that cedar had the highest VOC emissions of common sauna woods, while aspen had the lowest. Neither exceeded safety thresholds, but individual sensitivity varies.
What the builders told me
I asked three sauna builders what they use in their own saunas. Two said cedar. One said spruce. All three said the same thing about installation: leave a gap between the tongue and groove panels. Wood expands when it gets hot. If you install it tight, the panels will buckle.
They also said to use stainless steel fasteners, not galvanized. Galvanized hardware will corrode in the heat and moisture. Stainless does not.
How to decide
If you are building a sauna right now, here is your decision tree:
- Can you afford cedar? If yes, buy cedar.
- If not, buy hemlock or Nordic spruce.
- Do you have respiratory sensitivities? Buy aspen.
- Are you in a humid climate with imperfect ventilation? Cedar is worth the premium.
Do not overthink this. Any of these four woods will work well. The differences are real but not dramatic. A well-built sauna with good ventilation will perform well with any of them.
The wood matters. But the build quality matters more.
Frequently asked questions
What is the best wood for a sauna interior?
Western red cedar is the most popular choice in North America because it stays cool to the touch, resists rot naturally, and has low resin content. Nordic spruce is the traditional Finnish option, hemlock is a cost-effective alternative at roughly half the price of cedar, and aspen suits people with chemical sensitivities or respiratory issues.
Why should you avoid pine in a sauna?
Pine contains high amounts of resin that bleed out when heated, leaving sticky sap on your skin and producing a strong smell that becomes overwhelming. The resin can also cause skin irritation for some people, making pine a poor choice regardless of its low cost and wide availability.
Which sauna wood is best for people with allergies or chemical sensitivities?
Aspen is the recommended option because it has no scent, no resin, and very low VOC emissions when heated. A 2017 study in the Journal of Wood Science found that aspen had the lowest VOC emissions of the common sauna woods tested, and many public saunas in Europe use it for the benches for this reason.
Do sauna wood types release harmful compounds when heated?
Most common sauna woods release volatile organic compounds when heated, such as cedrol and thujaplicins from cedar and pinene and limonene from spruce. The 2017 study in the Journal of Wood Science found that neither cedar nor aspen exceeded safety thresholds, though individual sensitivity varies and aspen releases the least of the woods studied.