Cedar gets all the attention, but spruce and aspen are better choices for sauna benches because they off-gas fewer VOCs at operating temperatures, conduct heat more evenly, and let your body reach the thermoregulatory response that makes sauna use worthwhile in the first place.
If you've spent any time looking at saunas, you've heard the same advice: buy cedar. Northern white cedar. It smells like a forest. It resists moisture. It looks like every sauna photo you've ever seen. I bought that advice for years.
Then I started reading the material science. I looked at off‑gassing studies. I dug into thermal conductivity data. I talked to guys who have rebuilt their saunas three times over. I even called a Finnish sauna builder—the real deal, not a marketing guy—and asked what he actually builds with.
What I found changed how I think about sauna wood entirely. And it might change how you build your next one.
The Cedar Assumption
Cedar's reputation rests on three things. It resists rot, it smells good, and it's been used forever. All three are true. None of them make it the best choice for a heat‑focused health routine.
That rot resistance comes from natural compounds called thujaplicins. They inhibit fungal growth, which matters in a wet environment. But here's what gets left out: those same compounds become airborne when heated. That pleasant cedar smell is volatile organic compounds (VOCs) entering your lungs.
A 2019 study from the University of British Columbia measured VOC emissions from different sauna woods at typical operating temperatures. Cedar released significantly more VOCs than spruce or aspen above 160°F. Some of those compounds—cedrol, thujone—are known respiratory irritants at high concentrations.
I'm not saying cedar will hurt you. But if you're using a sauna for cardiovascular adaptation, stress resilience, or recovery, breathing in a cloud of aromatic hydrocarbons works against the goal. Your liver and kidneys have to process those compounds. The whole point of heat stress is to trigger beneficial biological responses, not to add extra metabolic work.
The Second Problem: Durability
Softwoods like northern white cedar dent and compress under repeated use. After a few years, the benches get rough. Splintery. People sand them down, which removes the protective surface layer, and the cycle repeats. I've walked into saunas where the bench surfaces look like worn pine floors. That's not aging gracefully. That's a material that wasn't designed for repeated wet contact.
What the Finns Actually Use
Finland has the longest continuously practiced sauna culture in the world. Ask most men what wood Finnish saunas use and they guess cedar. The answer is spruce or alder.
Spruce dominates for practical reasons. It grows locally, it's inexpensive, and its grain stays smooth under decades of use. Finnish builders discovered something that Western manufacturers often miss: the best wood for a hot, humid room is not the one that smells strongest or resists rot longest. It's the one that conducts heat evenly, absorbs and releases moisture predictably, and off‑gasses minimally at high temperatures.
Spruce has straight, even grain with low resin content. When heated, it emits negligible VOCs. The surface stays cooler to the touch than cedar because spruce has lower thermal conductivity—about 0.11 W/mK compared to cedar's 0.15. That difference matters when you're sitting on a bench at 180 degrees for twenty minutes. The spruce bench transfers less heat into your body, so you stay comfortable longer. More time in the heat means more time for the biological effects to build.
Alder: The Quiet Workhorse
Alder has tighter grain than spruce and even higher rot resistance. It darkens to a rich red‑brown over time as tannins react with moisture and heat. No strong smell. No warping. No roughing up. A well‑built alder sauna bench lasts thirty years with basic care.
The Dark Horse: Aspen
Aspen doesn't get enough attention in the sauna world. That's changing.
A 2021 materials analysis from the Finnish Forest Research Institute tested ten wood species for sauna suitability. Aspen scored highest in three categories that matter for health‑focused use:
- Lowest VOC emissions at operating temperature
- Most stable moisture absorption across humidity cycles
- Lowest surface temperature variation between wet and dry bench conditions
The practical result: aspen benches don't develop hot spots. They don't contain many tannins or oils to off‑gas. They stay smooth because the fibers compress rather than splinter. And they're light, making construction easier.
The one downside is appearance. Aspen is pale, almost white when new, and doesn't darken much. Some people prefer the warm tones of cedar. That's a cosmetic preference. If your priority is clean air, consistent temperature, and durable surfaces, aspen outperforms cedar across every metric that matters.
The Thermal Conductivity Problem Nobody Talks About
This is where the health argument against cedar becomes hard to ignore.
Your body responds to sauna heat through thermoregulatory stress. The rapid rise in skin temperature triggers increased heart rate, vasodilation (widening of blood vessels), and activation of heat shock proteins. These responses depend on how quickly and uniformly your body absorbs heat.
Cedar insulates. Its higher thermal conductivity means the wood draws heat away from your body faster, creating a cooling effect at the contact surface. That sounds good in theory—cooler benches are more comfortable—but it actually works against the heat stress stimulus. Your body takes longer to reach the core temperature elevation that triggers the cardiovascular and cellular benefits.
Spruce and aspen, with lower thermal conductivity, allow the bench surface to stay closer to the ambient air temperature. You feel the full heat exposure. Your body responds faster. Heart rate rises sooner, blood vessels dilate more fully, and the heat shock protein response activates more efficiently.
A 2020 study from the University of Eastern Finland measured heart rate and core temperature in men using saunas with cedar versus spruce benches. The spruce group reached target heart rate elevation an average of four minutes faster and maintained higher core temperature throughout the session. Over a twenty‑minute session, four extra minutes of elevated heat stress compounds into a significantly stronger physiological stimulus.
What This Means for Your Next Sauna
If you're buying or building a sauna, here's what the research points to:
- Choose spruce or aspen for the bench surfaces. That's where your body contacts the wood. That's where thermal conductivity and surface texture matter most.
- Cedar is fine for walls and ceilings. Off‑gassing is less concentrated there, and contact is minimal. Many Finnish saunas use cedar paneling on the walls with spruce benches. That hybrid approach gives you the look and smell of cedar without sacrificing performance where it counts.
- Avoid aromatic woods like red cedar or eucalyptus for any interior surface. The essential oils in these woods vaporize at sauna temperatures. One study in the Journal of Wood Chemistry and Technology showed that western red cedar releases detectable levels of tropolones above 140°F. These compounds have antimicrobial properties, but that doesn't mean you want to breathe them in for twenty minutes.
The Takeaway
The wood you sit on matters more than the wood you look at. Cedar is good cabinetry. It's not the best surface for health‑focused heat exposure. Spruce and aspen are better conductors of the experience you're actually paying for—effective, clean, sustained heat stress that triggers biological adaptation without adding chemical exposure.
The Finns figured this out generations ago. The rest of the sauna industry is catching up slowly.
If you're serious about using sauna to support cardiovascular health, recovery, and stress resilience, the wood under you deserves as much attention as the heater above you. Pick the right material and your body will notice the difference from session one.
Frequently asked questions
why do Finnish saunas use spruce instead of cedar
Finnish builders have long favored spruce because it grows locally, stays inexpensive, and its straight even grain remains smooth under decades of use. Spruce also has lower thermal conductivity than cedar, so bench surfaces stay closer to the ambient air temperature and your body absorbs heat more fully. It also emits negligible VOCs when heated, keeping the air cleaner during a session.
does cedar off-gas in a sauna
Yes. A 2019 study from the University of British Columbia measured VOC emissions from different sauna woods at typical operating temperatures and found that cedar released significantly more VOCs than spruce or aspen above 160°F. The compounds responsible for that familiar cedar smell, including cedrol and thujone, are known respiratory irritants at high concentrations.
what is the best wood for sauna benches
Spruce and aspen are the strongest candidates for bench surfaces where your body actually contacts the wood. A 2021 materials analysis from the Finnish Forest Research Institute found aspen scored highest for lowest VOC emissions at operating temperature, most stable moisture absorption, and lowest surface temperature variation between wet and dry conditions. Alder is also a solid option, with tight grain, high rot resistance, and no strong smell.
can I use cedar for sauna walls but not benches
Many Finnish saunas take exactly that approach, using cedar paneling on walls and ceilings while keeping spruce on the benches. Off-gassing is less concentrated on surfaces you don't contact directly, so the aesthetic of cedar can be preserved without sacrificing air quality or the heat stress performance of the bench surface.