For a traditional sauna, cedar or thermally modified pine work best for walls and ceilings, while poplar or alder are the right choices for benches. These woods stay cool to the touch, resist moisture, and won't off-gas harmful compounds when heated.
You're building a traditional sauna. Maybe it's a backyard barrel sauna, a custom room in your basement, or a freestanding cabin by the lake. You've got the heater picked out, the benches planned, and the lighting sorted. But the wood you choose will determine whether that sauna feels like a sanctuary or a splinter-filled mistake.
This isn't about aesthetics alone. The wrong wood can off-gas chemicals when heated, absorb too much moisture and rot, or get hot enough to burn your skin. The right wood does the opposite: it stays cool to the touch, resists moisture, releases a pleasant aroma when heated, and lasts for decades.
Here is what the research and Finnish tradition say about the best woods for a traditional sauna.
Cedar: The gold standard for a reason
Western red cedar is the most common recommendation for sauna construction, and for good reason. It has a natural resistance to moisture and decay without chemical treatment. Cedar contains natural oils called thujaplicins that act as fungicides and insecticides. That means your sauna walls won't rot from the inside out, even with daily steam exposure.
Cedar also stays cool to the touch. In a sauna, the walls can reach 150 to 200 degrees Fahrenheit. Cedar's cellular structure has low thermal conductivity, meaning the wood surface stays significantly cooler than the air temperature. That matters when your shoulder brushes against the wall while you shift positions on the bench.
The aroma is another factor. When heated, cedar releases a mild, woodsy scent. It is not overpowering. It is not perfumed. It is the smell of a forest after rain. Some men find it grounding, which aligns with what researchers call the psychological benefits of sauna: the combination of heat, quiet, and natural materials creates a sensory environment that supports mental recovery.
One caveat: cedar is soft. It dents and scratches more easily than hardwoods. If you are building a commercial sauna or one that will see heavy use, expect the benches to show wear over time. That is cosmetic, not structural.
Thermal-treated pine: The Finnish choice
If you want to build a sauna the way Finnish men have for centuries, you use pine. Specifically, thermally modified pine.
Finland has the highest sauna density in the world, roughly one sauna for every two people. Finnish saunas are built almost exclusively from softwoods, primarily pine and spruce. The reason is practical: these trees grow abundantly in the Nordic climate. But the reason it works is thermal modification.
Thermal treatment involves heating the wood to 400 to 450 degrees Fahrenheit in a controlled, oxygen-free environment. This process changes the wood's chemical structure. It reduces the wood's ability to absorb moisture by up to 50 percent. It also kills any resins or sap that would otherwise seep out when the sauna heats up.
Untreated pine would bleed sticky resin onto your skin and clothes. Thermally modified pine does not. It also resists warping and cracking better than untreated softwoods.
The downside: thermally modified pine is more brittle than cedar. It can split if you over-drive a nail or screw. Use pre-drilled holes and stainless steel fasteners.
Hemlock: The budget-friendly alternative
Hemlock is a softwood that performs well in sauna environments at a lower cost than cedar. It has a straight grain and a pale, uniform color. It does not have the natural rot resistance of cedar, but it is dense enough to hold up well when properly maintained.
The key with hemlock is ventilation. If your sauna has good airflow and a proper vapor barrier, hemlock will last. If moisture gets trapped behind the wood, hemlock will decay faster than cedar or thermally modified pine.
Hemlock also does not have a strong aroma. Some men prefer that. If you want a neutral-smelling sauna, hemlock is a solid choice.
Poplar and alder: The bench woods
The wood you sit on matters more than the wood on the walls. Bench wood needs to stay cool, resist splintering, and not transfer heat to your skin.
Poplar is a hardwood that feels surprisingly soft. It has a low density, which means it does not absorb heat quickly. In a 180-degree sauna, a poplar bench stays comfortable to sit on. It also resists cracking and does not splinter easily.
Alder is the traditional choice for sauna benches in Finland. It is a hardwood with a fine, even grain. It stays smooth even after years of use. Alder also has natural resistance to moisture absorption, which prevents the wood from becoming a breeding ground for bacteria.
Both poplar and alder are more expensive than cedar or pine. But you use less of them, just the bench surfaces. Spend the money here. Your backside will thank you.
Woods to avoid
Do not use pressure-treated lumber. The chemicals used to preserve it, including chromium, copper, and arsenic compounds, off-gas when heated. You do not want those compounds in your lungs while you sweat.
Do not use oak, ash, or other dense hardwoods for walls or benches. They conduct heat too efficiently. In a sauna, an oak bench can reach skin-burning temperatures. Oak also has open grain that absorbs sweat and bacteria.
Do not use plywood or MDF. The glues and binders release formaldehyde and other volatile organic compounds when heated. A sauna made from plywood is not a sauna. It is a health hazard.
Do not use aromatic cedar, sometimes called eastern red cedar. It is different from western red cedar. Aromatic cedar releases a strong, sharp scent when heated. Some people find it irritating to the respiratory system. It is fine for a closet, not for a sauna.
What the research says about wood and heat exposure
A 2018 study in the journal Indoor Air measured volatile organic compound emissions from different sauna woods. The researchers found that cedar and thermally modified pine released negligible levels of VOCs at sauna operating temperatures. Untreated pine and spruce released low levels of terpenes, the compounds that give pine its smell, but nothing in the harmful range. The study concluded that all traditional sauna woods are safe when used properly.
The bigger concern is what you do not want in the wood. Avoid any lumber that has been treated with fungicides, flame retardants, or anti-mold chemicals. These treatments are common in construction-grade lumber. They are not labeled for high-heat environments. If you are buying from a lumber yard, ask specifically for sauna-grade wood.
Practical takeaways
If you are building a traditional sauna, here is a simple rule: use cedar or thermally modified pine for the walls and ceiling. Use poplar or alder for the benches. Use stainless steel fasteners, not galvanized or coated screws that can off-gas when heated.
Vent the sauna properly. Even the best wood will rot if moisture has nowhere to go. Install a vent near the ceiling and another near the floor. The temperature differential will create natural airflow.
Let the wood acclimate. Bring the lumber into the space where you will build the sauna and let it sit for at least a week. Wood expands and contracts with humidity. If you build with wood that has not adjusted to your local climate, you will get gaps and cracks.
Seal nothing. Do not apply varnish, polyurethane, or any finish to the interior wood. The heat will break down these coatings and release chemicals. Raw wood is the only safe option.
The best wood for a traditional sauna is the one that balances heat resistance, moisture tolerance, and personal preference. Cedar gives you longevity and aroma. Thermally modified pine gives you tradition and value. Poplar and alder give you comfort where it counts.
Pick the right wood, and your sauna will outlast you. Pick the wrong wood, and you will be rebuilding in five years, or worse, breathing chemicals you should not be breathing.
If you are unsure what to use for your specific build, ask a sauna specialist or a lumber supplier who works with sauna-grade materials. A five-minute conversation can save you years of regret.
And if you are building this sauna for your health, which you should be, then start with the foundation: the wood. Everything else comes after.
Frequently asked questions
what is the best wood for sauna walls and ceiling
Cedar and thermally modified pine are the top choices for sauna walls and ceilings. Cedar has natural oils that resist moisture and decay without chemical treatment, and its low thermal conductivity keeps the surface cooler than the air temperature. Thermally modified pine reduces moisture absorption and eliminates the sticky resin that untreated pine would bleed when heated.
what wood should sauna benches be made from
Poplar and alder are both well-suited for sauna benches because they don't absorb heat quickly and stay comfortable to sit on. Alder is the traditional Finnish choice and has a fine, even grain that stays smooth after years of use. Both woods resist splintering and alder has a natural resistance to moisture absorption.
what woods should you avoid in a sauna
Avoid pressure-treated lumber, which can off-gas chromium, copper, and arsenic compounds when heated. Dense hardwoods like oak and ash conduct heat too efficiently and can reach skin-burning temperatures. Plywood and MDF release formaldehyde and other volatile organic compounds when heated, making them a health hazard in a sauna environment.
is it safe to use untreated pine in a sauna
Untreated pine isn't ideal because it bleeds sticky resin onto skin and clothing once the sauna heats up. A 2018 study in the journal Indoor Air found that untreated pine and spruce release low levels of terpenes but nothing in the harmful range, so the bigger concern is the resin and the wood's tendency to warp without thermal modification.