Cedar vs. Hemlock vs. Thermowood: Which is Best for Your Sauna?
You’ve decided to build a sauna. Maybe you’ve already picked the room, settled on the heater, and pictured exactly how it’s going to feel after a long week. But then someone asks: what wood are you using?
And just like that, you’re down a rabbit hole comparing cedar vs. hemlock vs. thermowood, reading forum threads that contradict each other, and wondering if this decision matters as much as everyone claims it does.
It does. The wood you choose for your sauna affects how it smells, how it feels to the touch, how long it lasts, and even the air you’re breathing while you use it. For a high-end residential sauna — the kind that gets used daily and is meant to last decades — this isn’t a decision to make based on whatever’s in stock at the lumber yard.
This guide breaks down the three most popular premium sauna woods: Western Red Cedar, Western Hemlock, and Thermowood. We’ll compare them honestly across durability, off-gassing, and thermal properties, then give you a clear framework for making the right call for your project.
Understanding the Role of Wood in Saunas
A sauna isn’t just a hot room. It’s a carefully controlled thermal environment that cycles through extreme heat, steam (in traditional Finnish-style saunas), and cooling — often multiple times per session, multiple times per week. The wood used for the benches, walls, and ceiling takes the brunt of all of it.
Good sauna wood needs to do several things simultaneously:
- Stay cool enough to touch even when ambient temperatures reach 180–195°F
- Resist warping, cracking, and checking under repeated thermal stress
- Handle moisture without rotting, swelling, or harboring bacteria
- Off-gas minimally so the air inside stays clean and non-irritating
- Feel good — both aesthetically and physically against bare skin
The thermal and structural properties of wood aren’t just comfort factors. They’re also efficiency factors. A wood that absorbs and holds heat poorly makes your heater work harder. A wood that warps after two seasons means you’re replacing benches before the sauna even breaks in.
With that context, let’s look at each material.
Cedar Wood: Features and Benefits
Western Red Cedar is the classic sauna wood, and there’s a reason it’s held that status for decades. It’s naturally resistant to decay, dimensionally stable under heat, and has a distinctive warm aroma that many people associate with the sauna experience itself.
Why Cedar Works Well in Saunas
Cedar’s open grain structure gives it a naturally low density, which translates directly to lower thermal conductivity. In simple terms: cedar surfaces stay cooler to the touch even when the room is very hot. That matters when you’re sitting bare-skinned on a bench at 190°F.
Cedar also contains natural oils that inhibit mold and bacterial growth — a major advantage in the moisture-heavy sauna environment. These same oils contribute to its aromatic quality, which many sauna enthusiasts love.
The Off-Gassing Question
Here’s where cedar gets more complicated. Those natural oils and resins are also what cedar off-gasses as it heats up. For most people, this is simply “that sauna smell.” But for individuals with cedar allergies, respiratory sensitivities, or strong preferences for neutral air quality, the aromatic compounds can be irritating.
Cedar’s off-gassing is natural — it’s not synthetic chemicals — but it’s not neutral either. If clean, scent-free air is a priority for health or preference reasons, cedar’s aromatics are worth weighing carefully.
Longevity
In a well-maintained sauna, cedar can last 20–30 years before showing significant wear. Its natural decay resistance means it handles moisture better than most unmodified softwoods. However, over time, the oils that protect it do leach out, and the wood can darken and become more porous. Occasional light sanding of bench surfaces helps maintain the wood and manage off-gassing as it ages.
Hemlock for Saunas: Pros and Cons
Western Hemlock doesn’t have the name recognition of cedar in the sauna world, but it’s a legitimate — and in some ways superior — choice for certain applications.
The Case for Hemlock
Hemlock is nearly odorless when heated. This is its single biggest advantage for sauna use. If you or a family member has sensitivities to aromatic compounds, or if you simply prefer a clean sensory environment without a wood scent, hemlock delivers that without compromise.
It’s also a light-colored, fine-grained wood that takes on a pleasant, almost creamy appearance. Many custom sauna builders use hemlock precisely because it photographs beautifully and provides a clean, Scandinavian-inspired aesthetic that cedar can’t quite match.
In terms of workability, hemlock machines cleanly, holds tight tolerances, and is easy to sand smooth. For custom millwork — especially on bench slats and backrests where surface quality really matters — hemlock is easy to work with.
Where Hemlock Falls Short
Hemlock is less naturally rot-resistant than cedar. It doesn’t have the same natural oils, which means it’s more vulnerable to moisture damage over time if the sauna isn’t properly ventilated. In a well-designed sauna with adequate airflow and a proper post-session drying routine, this is manageable. In a poorly ventilated space, hemlock will degrade faster than cedar.
It’s also slightly denser than cedar, which means slightly higher thermal conductivity. The difference is real but modest — hemlock bench surfaces can feel marginally warmer to the touch than cedar under equivalent conditions, though this varies with thickness and airflow.
Cost Position
Hemlock is generally less expensive than cedar, which makes it a practical choice for larger sauna interiors where material costs add up quickly. Some builders use hemlock for walls and ceiling while specifying cedar or thermowood for the benches — a hybrid approach that balances cost and performance.
The Increasing Popularity of Thermowood
Thermowood is the newest of the three options in mainstream sauna construction, and it’s generating significant interest among builders who want performance without compromise.
What Is Thermowood?
Thermowood is not a species — it’s a process. Softwood (most commonly Scandinavian spruce or pine) is heat-treated in a controlled, high-temperature environment (typically between 374–428°F) using steam and heat, with no chemicals involved. This process fundamentally changes the wood’s cellular structure.
The result is a wood that behaves very differently from its untreated counterpart:
- Reduced moisture absorption — the wood becomes more dimensionally stable.
- Lower density — thermal conductivity decreases, meaning surfaces stay cooler.
- Near-zero off-gassing — the heat treatment drives off the volatile compounds that would otherwise off-gas in sauna conditions
- Improved durability — the treated wood resists decay significantly better than untreated softwood.
The process is entirely physical — no adhesives, no chemical preservatives. This is what makes thermowood attractive from both a health and an environmental standpoint.
Thermal Performance
Of the three options, thermowood typically has the lowest thermal conductivity. This is a meaningful performance advantage for benches in particular. Thermowood bench surfaces tend to feel the coolest to the touch, which directly affects comfort at high temperatures. For users who prefer very high heat sessions or for saunas with powerful heaters, this margin matters.
Off-Gassing Profile
Thermowood’s off-gassing profile is as close to neutral as you’ll get in a natural wood. The heat treatment process effectively pre-treats the wood, driving off the volatile organic compounds before the wood ever enters your sauna. For health-conscious clients or those with chemical sensitivities, thermowood is often the first recommendation.
Durability Comparison
Wood | Natural Rot Resistance | Dimensional Stability | Expected Lifespan (Well-Maintained) |
Western Red Cedar | High | Good | 20–30 years |
Western Hemlock | Moderate | Moderate | 15–25 years |
Thermowood | High (process-enhanced) | Excellent | 25–35 years |
Thermowood’s heat treatment significantly reduces its equilibrium moisture content — the point at which the wood stabilizes relative to ambient humidity. This means thermowood is less prone to the repeated swelling and shrinking that eventually causes checking and warping in sauna conditions. Over a long service life, this dimensional stability is a real advantage.
Cedar holds up well due to its natural oils, but those oils do diminish over time. Hemlock, without that natural protection, requires the most attention to ventilation and maintenance to reach its full potential lifespan.
Off-Gassing and Health Considerations
This topic matters more than many sauna buyers realize. In a small, enclosed, high-temperature space, you’re breathing whatever the wood releases — concentrated by heat and limited airflow.
Cedar off-gasses natural terpenes and aromatic oils. These are not synthetic VOCs, but they are bioactive compounds. Most people tolerate them well, and many actively enjoy the scent. However, plicatic acid — found in Western Red Cedar — is a known sensitizer that can trigger respiratory reactions in some individuals with repeated exposure.
Hemlock is nearly inert when heated. Its low aromatic oil content means very little is released into the air. This makes hemlock arguably the safest choice for individuals with any respiratory concerns, though its profile is less studied than cedar’s simply because cedar has a longer history of use and scrutiny.
Thermowood has the cleanest off-gassing profile of the three. The pre-treatment process removes volatile compounds from the wood before it’s installed. In practice, thermowood in a sauna produces very little scent or off-gassing, even when new.
For families where someone has allergies, asthma, or chemical sensitivities, hemlock and thermowood are the stronger choices. Cedar is the right call when the aromatic experience is desired, and no sensitivities exist.
Thermal Properties of Each Wood Type
Thermal conductivity determines how quickly heat moves through a material. In sauna bench design, lower conductivity means cooler surfaces — which means more comfortable contact at high temperatures.
- Cedar: Low thermal conductivity, open-grained structure. Surfaces stay comfortably cool at standard sauna temperatures. A benchmark wood for sauna thermal performance.
- Hemlock: Slightly higher density than cedar, slightly higher conductivity. The difference is modest in practice but measurable.
- Thermowood: Heat treatment removes bound water from the wood’s cell walls, reducing density and conductivity. Thermowood typically outperforms both cedar and untreated hemlock in surface temperature at equivalent conditions.
For energy efficiency, better-insulating bench wood means less of the sauna’s heat energy is absorbed by the structure itself, keeping air temperature more consistent. The differences between these three options aren’t dramatic enough to significantly change heater sizing, but in a well-optimized custom sauna, thermowood’s lower conductivity contributes to overall efficiency.
Cost Analysis for Sauna Projects
Material costs shift with market conditions, but here’s a general framework:
Western Red Cedar is typically mid-to-high in cost. Premium grades (clear, knot-free) command a significant premium and are what you want for sauna applications — knots are resin pockets that off-gas heavily and can be uncomfortable if they end up on a bench surface.
Western Hemlock is generally the most affordable of the three for comparable grades. Its cost advantage makes it attractive for larger interior volumes where you’re covering significant wall and ceiling area.
Thermowood carries a premium over both. The heat treatment process adds cost, and much of the supply is imported (primarily from Scandinavia and Finland). For a full sauna interior, expect thermowood to run noticeably higher than hemlock and modestly higher than cedar.
A practical approach many custom sauna builders use: specify thermowood or premium cedar for the benches — where thermal comfort and off-gassing matter most — and use hemlock for walls and ceiling to manage overall project cost without compromising the user experience.
Environmental and Sustainability Considerations
All three options can be sourced responsibly, but their sustainability profiles differ.
Cedar from responsibly managed Pacific Northwest forests is generally considered a sustainable choice. Look for FSC (Forest Stewardship Council) certification when sourcing. Old-growth cedar is increasingly scarce; most commercial cedar today is second-growth, which varies more in quality and grain consistency.
Hemlock is abundant and fast-growing relative to many alternatives. It’s broadly considered a sustainable species when sourced from certified forests. Its lower cost partly reflects its relative abundance.
Thermowood earns its environmental reputation from the process itself: no chemical preservatives, no adhesives, and the starting material is typically spruce or pine — fast-growing, widely available species. The trade-off is the energy cost of the heat treatment process, though this is generally considered offset by the extended product lifespan.
If sustainability certifications are important to your project, verify them at the supplier level regardless of species — certification applies to sourcing and chain of custody, not to the wood type itself.
Key Takeaways for Choosing the Right Wood
Here’s a simple decision framework:
- Choose Cedar if you value the traditional sauna aesthetic and aroma, have no respiratory sensitivities, and want proven long-term performance with widely available supply.
- Choose Hemlock if budget is a significant factor, you prefer a neutral scent environment, or you’re covering large surface areas where cost per board foot adds up.
- Choose Thermowood if you want the cleanest air quality, best dimensional stability, and highest thermal performance — and you’re willing to pay the premium for it.
- Consider a hybrid approach — thermowood or cedar benches, hemlock walls and ceiling — for projects where both budget and performance are important.
Key Takeaways
- Cedar offers natural decay resistance and a classic aromatic experience but can trigger sensitivities in some users.
- Hemlock is nearly odorless when heated, cost-effective, and easy to work with — but requires better ventilation to maximize its lifespan.
- Thermowood delivers superior thermal performance, near-zero off-gassing, and excellent dimensional stability through a chemical-free heat treatment process.
- Off-gassing matters: in a small, enclosed sauna, what the wood releases is concentrated in the air you breathe.
- Thermal conductivity directly affects bench comfort — lower is better for contact surfaces.
- Hybrid builds (thermowood or cedar benches + hemlock walls) are a smart way to balance performance and cost.
- Verify sustainability certifications at the supplier level for any species.
FAQs
1. What is the durability of Thermowood compared to Cedar?
Thermowood and cedar are both highly durable in sauna conditions, but for different reasons. Cedar relies on its natural oils to resist decay. Thermowood’s durability comes from the structural changes induced by the heat treatment process, which reduces the wood’s moisture content and makes it inhospitable to the fungi that cause rot. In sauna conditions specifically — repeated heat and moisture cycles — thermowood’s superior dimensional stability gives it a potential edge in long-term performance, though both options can last 20–30+ years with proper care.
2. Which wood is least likely to warp or crack in a sauna?
Thermowood is the most dimensionally stable of the three. The heat treatment process dramatically reduces the wood’s tendency to absorb and release moisture — the primary driver of warping and checking. Cedar is the next most stable, followed by hemlock. For benches and other horizontal surfaces that take the most thermal stress, thermowood is the top choice for warp resistance.
3. Are there any health risks associated with off-gassing from these woods?
Cedar’s natural aromatic compounds — particularly phellandrene — are known sensitizers. Most users experience no issues, but people with existing respiratory conditions or repeated high-level exposure may develop sensitivities over time. Hemlock off-gasses very little and is well-tolerated by most users. Thermowood’s off-gassing is minimal thanks to pre-treatment. None of these woods present the kind of VOC concerns associated with composite materials or chemically treated lumber, but for health-sensitive users, hemlock and thermowood are the lower-risk choices.
4. Why is Thermowood considered environmentally friendly?
The heat treatment process uses only heat and steam — no chemical preservatives or adhesives. The base material is typically spruce or pine, both fast-growing and widely available species. The extended product lifespan also means less frequent replacement. The trade-off is the energy required for the treatment process itself, but this is generally considered reasonable relative to the performance gains and avoided use of chemical treatments.
5. Can the choice of wood affect sauna energy costs?
Yes, though the effect is modest. Woods with lower thermal conductivity — cedar and especially thermowood — absorb less heat from the sauna’s air mass into the bench and wall structure. This means the heater maintains the target temperature more efficiently. In practice, the difference between cedar and thermowood won’t change your electricity bill dramatically, but over years of regular use, the cumulative efficiency difference is real. Proper insulation and heater sizing have a larger impact on energy efficiency, but wood choice is a contributing factor.
6. What is the best wood for saunas if budget isn't a concern?
For most high-end applications, thermowood offers the best combination of thermal performance, air quality, dimensional stability, and durability. Cedar is a close second with the advantage of a proven track record and availability. If the aromatic experience matters to you, cedar may actually be the preferred choice despite thermowood’s technical advantages.
7. Can I mix wood species in a single sauna build?
Yes, and many premium sauna builders do exactly this. A common approach is to use thermowood or high-grade cedar for bench surfaces — where thermal performance and off-gassing matter most — and hemlock for walls, ceiling, and structural elements where cost efficiency is more important. The visual contrast between species is usually subtle, especially as the woods age, and the functional benefits of the hybrid approach are real.
8. How long does cedar last in a sauna?
In a well-designed sauna with adequate ventilation and regular use and maintenance, high-grade Western Red Cedar can last 20–30 years. Over time, the wood’s natural oils leach out, the surface darkens, and the wood becomes more porous. Light periodic sanding of bench surfaces helps maintain the wood and reduce off-gassing from older, more degraded material. Replacing bench slats every 10–15 years is common even when the broader structure remains sound.
