Thermowood vs Cedar Sauna: Which is the Right One for You?

Choosing the right wood for your sauna is one of the more consequential decisions in the build process. Get it right, and you’ll have an interior that holds up for decades with minimal fuss. Get it wrong, and you’re looking at warped bench slats, surface checking, or a maintenance routine that feels like a second job. Thermowood and cedar are the two materials most buyers land on, and the thermowood vs cedar comparison is genuinely close enough that the right answer depends on your specific situation.

This guide covers the pros and cons of each material, including durability, aesthetics, maintenance requirements, and suitability for different climates and sauna types. Whether you’re planning your first sauna build or replacing an aging interior, this guide gives you the trade-offs you need to decide with confidence.

Overview of Thermowood

Thermowood offers superior dimensional stability and lower long-term maintenance. Cedar delivers a lower upfront cost and a classic aromatic sauna experience. The right choice depends on your climate, budget, and how often you’ll use the sauna.

Thermowood is lumber kiln-dried at high temperatures in a steam-and-heat process that permanently alters the wood’s cell structure. This thermally modified process, not a chemical treatment, gives thermowood enhanced stability and rot resistance.

The best-selling thermowood sauna product in North America is Thermory, an Estonian thermowood producer whose products are specified in many North American sauna kits. Thermory heat-treats pine, aspen, and spruce to ThermoWood process standards. When you see “Thermory spruce” or “Thermory aspen” in sauna kit listings, it refers to species-specific thermowood produced under this brand. The process itself was commercialized in Finland in the 1990s and is now governed by the Finnish ThermoWood Association, which certifies products bearing the ThermoWood trademark. The underlying research was pioneered by the VTT Technical Research Centre of Finland.

Are Thermowoods Good for Saunas?

Thermowood has become a popular choice for sauna construction, offering a practical alternative to traditional cedar. Below is a straightforward breakdown of thermowood’s strengths and weaknesses.

Advantages of Thermowood

• Durability: Heat treatment permanently reduces the wood’s equilibrium moisture content (EMC), so thermowood resists swelling and shrinking even under the fluctuating temperatures and humidity of a sauna environment, and it holds its shape where untreated wood would warp or crack.
• Low Maintenance: Because thermowood’s EMC is significantly lower than untreated wood, it does not require the periodic oiling cedar needs to prevent surface checking. That’s a meaningful advantage for commercial operators or anyone who wants a set-and-forget interior. Its reduced moisture absorption also limits the risk of mold.
• Improved Aesthetics: Thermowood has a rich brown color that complements modern sauna designs. This tone deepens slightly over time, developing a warm, aged patina.
• Comfortable Feel: Thermowood offers a smooth, splinter-resistant surface that stays comfortable on bare skin even at high temperatures.
• Versatility: Thermowood’s dimensional stability makes it reliable across climates, including humid regions where aromatic red cedar can perform less consistently.
• Sauna Type Compatibility: Thermowood suits all sauna types, including dry, steam, and infrared saunas.

Disadvantages of Thermowood

• Higher Cost: Thermowood typically costs more per linear foot than comparable cedar grades, though this gap narrows over a longer ownership horizon when you factor in avoided maintenance costs.
• Less Traditional Look: Thermowood’s rich brown color deviates from the classic light wood tones many buyers associate with traditional sauna interiors.
• Limited Availability: Thermowood may not be as readily available as cedar in all regions.
• Scent: Thermowood has no natural aroma. Builders who want both materials’ benefits sometimes use thermowood for walls and ceiling while specifying cedar bench slats, a hybrid approach that captures the aromatic experience where it’s most noticeable.

Use Cases

Thermowood is a strong choice for:

• High-use saunas: Gyms, commercial spas, or frequently used home saunas benefit from thermowood’s resistance to wear and repeated wet-dry cycles.
• Humid climates: In high-humidity areas, thermowood’s stability makes it a more reliable long-term option than cedar.
• Modern sauna designs: Thermowood’s rich brown color complements contemporary sauna aesthetics.

How is Thermowood Made? The Heat Treatment Process Explained

Thermowood is not a species. It’s softwood lumber permanently modified through a three-stage industrial heat treatment process developed in Finland in the 1990s. The VTT Technical Research Centre of Finland pioneered the process, and the Finnish ThermoWood Association holds the ThermoWood trademark.

The treatment works in three stages. First, the wood is rapidly heated and dried using steam to prevent surface cracking. Second, the temperature is raised to a high level in a low-oxygen, steam-saturated environment. This is the modification stage where the wood’s cell structure is permanently altered. Third, the wood is slowly cooled and re-moisturized to bring it back to a workable state.

For sauna builders, this matters because of what it does to the wood’s chemistry. The high heat breaks down the hemicellulose in the wood’s cell walls, the component most responsible for absorbing and releasing moisture. The result is a dramatic reduction in EMC, which directly limits the swelling, shrinking, and warping that sauna heating cycles would otherwise cause.

The ThermoWood process produces two main grades: Thermo-S (stability-focused) and Thermo-D (durability-focused). Sauna interiors typically use Thermo-S; outdoor structural applications call for Thermo-D.

The entire process is chemical-free. No preservatives, adhesives, or synthetic treatments are introduced at any stage, which is why thermowood carries a Class D durability rating and is considered safe for high-temperature, skin-contact environments like sauna benches and wall cladding. Thermory, one of the world’s largest thermowood producers, uses the same three-stage process and is the brand most commonly specified in North American sauna kit manufacturing.

If you’ve seen the term “thermo ayous” in sauna product listings, it refers to African Ayous (Obeche) wood that has undergone the same heat-treatment process. It’s a lighter-colored option gaining traction as a thermowood sauna species.

What Types of Thermowoods are Used for Saunas?

Thermowood can be produced from various softwoods, each offering slightly different characteristics. Here are the most common types used for saunas.

• Thermowood Pine: Thermowood pine is the entry-level thermowood option and suits wall and ceiling cladding. Its treated color ranges from golden-brown to medium brown, and it holds its shape well through a steam sauna’s wet-dry cycles. Thermory pine is the entry-level thermowood SKU most commonly found in pre-built sauna kits.

• Thermowood Aspen: Aspen’s naturally low resin content means it stays cool to the touch even at high bench temperatures, a practical advantage for benches and backrests where skin contact is constant. Thermowood Aspen is the closest thermowood equivalent to the feel of traditional Finnish sauna wood, and its light tone creates a bright, airy interior. Thermory aspen is the species used in several SaunaLife and Dundalk Leisurecraft sauna models. It is preferred for bench slats because its surface stays cooler than cedar at equivalent ambient temperatures.
• Thermowood Spruce: Spruce has a tighter grain than pine, which gives it a slightly smoother finished surface. Thermory spruce is the species referenced in the SaunaLife CL7G and similar premium outdoor sauna kits. Its tighter grain produces a cleaner finished surface than pine, making it the preferred choice for visible wall cladding in high-end builds.
• Thermowood Alder: Alder’s very low density means it heats up faster than pine or spruce and stays cooler on the surface, a practical advantage for bench construction in high-temperature Finnish-style saunas. It is often used as a premium alternative to aspen.
• Thermo Aspen (Thermory Aspen): Already covered above, but worth noting that Thermory aspen sits in the mid-range of thermowood pricing and is the species most commonly specified for bench slats in quality kit construction.

Is Cedar Good for Saunas?

Cedar is a proven sauna wood with a long track record, but not all cedar is the same, and the species you choose matters more than most buyers realize.

Advantages of Cedar

• Natural Fragrance: Cedar’s aroma comes from thujaplicin, a natural oil that also contributes to its antimicrobial and insect-repellent properties. This oil gradually diminishes with age and heavy use, but for many sauna enthusiasts it remains an integral part of the experience.
• Moisture Resistance: Cedar naturally resists moisture and mildew growth, making it well-suited for sauna environments.
• Insulation: Cedar offers good insulation, helping retain heat in the sauna.
• Comfortable Feel: Cedar has a smooth texture that feels pleasant on bare skin, even at high sauna temperatures.
• Aesthetics: Cedar’s light wood tone adds a natural, classic look to any sauna design.
• Versatility: Cedar works well in dry, steam, and infrared saunas.
• Affordability: Compared to thermowood, cedar is generally a more affordable upfront option.

Cedar Species Comparison

Not all cedar performs identically in a sauna environment. Here’s how the three most common species compare:

• Western Red Cedar (Thuja plicata): The most common sauna cedar in North America. Lightweight, aromatic red cedar with natural resistance to decay. Grades range from clear (knot-free, premium) to knotty (more affordable). Western Red Cedar is widely available across the US and Canada, including from suppliers in Delta, BC, Canada, a major production hub for this species.
• Eastern White Cedar (Thuja occidentalis): Denser and slightly less aromatic than Western Red Cedar. More commonly available in the northeastern US and Canada. A solid option where Western Red Cedar is scarce or where a tighter grain is preferred.
• Alaskan Yellow Cedar (Cupressus nootkatensis): The most durable cedar species, with natural oils that rival thermowood’s rot resistance. Significantly more expensive than Western Red Cedar but can provide many years of service in a well-maintained sauna.

Disadvantages

• Maintenance: Cedar requires regular cleaning and occasional oiling to maintain its properties and appearance. Use a sauna-specific cedar oil or diluted tung oil. Avoid petroleum-based sealers, which can off-gas at sauna temperatures.
• Warping: Cedar is more susceptible to warping in high-humidity environments than thermowood. Without regular oiling and cleaning, surface checking and graying can appear well before the wood reaches its natural lifespan.
• Durability: Cedar is durable, but it does not match thermowood’s longevity in high-use or high-humidity conditions.
• Limited Availability: Certain cedar grades and species, particularly clear-grade Western Red Cedar, may have limited availability in some regions.

Use Cases

Cedar remains a strong choice for saunas in many situations, particularly:

• Home Sauna Kits: For personal or family use, cedar offers a well-rounded balance of affordability, aesthetics, and performance. Browse our cedar sauna kits to see what’s available at different price points.
• Dry Saunas: Cedar’s natural moisture resistance makes it well-suited for dry sauna environments.
• Traditional-Style Saunas: Cedar’s classic look and natural thujaplicin aroma create a timeless, authentic sauna experience.

Cedar might not be the best choice for:

• High-use saunas: In gyms or commercial settings with frequent use, thermowood’s superior durability is more practical.
• Humid climates: In areas with very high humidity, cedar’s susceptibility to warping and surface checking is a real concern.
• Those who prefer low maintenance: If minimal upkeep is a priority, thermowood’s reduced need for oiling is a meaningful advantage.

Thermowood vs Cedar: Side-by-Side Comparison

Choosing between thermowood and cedar depends on your priorities. Here’s a table summarizing the key differences.

A quick guideline to help you decide

• Prioritize durability and low maintenance: Choose thermowood.
• For affordability and a classic look, choose cedar.
• For a modern aesthetic and reliable performance in any climate, thermowood is worth the higher upfront cost.
• For a home sauna used occasionally, Cedar can be a practical choice.

Climate note:

If you’re in a coastal or high-humidity region and plan to use your sauna daily, thermowood’s lower equilibrium moisture content is the single most important performance differentiator. This matters especially for buyers in the Pacific Northwest, the Southeast US, and other areas where ambient humidity stays high year-round. Cedar can perform well in drier climates with less extreme humidity swings.

Thermowood vs Cedar: Cost Comparison

Thermowood generally costs more upfront than cedar, but the long-term total cost of ownership is closer than the sticker price suggests.

On a per-linear-foot basis, entry-level thermowood pine and knotty cedar are roughly comparable, while premium thermowood species (spruce, aspen, alder) cost more than clear-grade cedar. The gap narrows further when you account for maintenance.

Cedar requires periodic oiling to prevent surface checking. Thermowood requires no oiling. Over years of regular sauna use, the avoided maintenance cost and effort adds up in thermowood’s favor.

The upfront cost gap between thermowood and mid-grade cedar is narrower than most buyers expect. Thermowood’s real cost advantage is reduced maintenance and a longer lifespan. If you’re building a sauna you plan to use daily or leave outdoors year-round, the total cost of ownership calculation tends to favor thermowood. If you’re building a home sauna for occasional use and you’re comfortable with a regular maintenance routine, knotty cedar remains a genuinely competitive option.

For a full range of outdoor sauna kits in both materials, browse our catalog or reach out and we’ll help you spec the right build for your climate and budget.

Thermowood vs Cedar: Which Lasts Longer?

In a well-maintained home sauna, thermowood interiors typically outlast Western Red Cedar interiors by a meaningful margin. The gap widens in high-use or high-humidity environments.

Cedar’s longevity depends heavily on a consistent maintenance schedule. Skip that maintenance and surface checking, and gapping, warping, and eventual cracking can appear well ahead of schedule in a heavily used sauna. Thermowood, by contrast, requires no oiling and holds its structural integrity through repeated wet-dry cycles because its equilibrium moisture content is already so low.

Sauna type also plays a role. In a dry sauna, cedar performs closer to its upper lifespan range because the humidity swings are less severe. In a steam sauna, constant moisture exposure accelerates surface checking in cedar and makes thermowood’s low EMC a more decisive advantage. Alaskan Yellow Cedar is the exception among cedar species. Its natural oils give it rot resistance that approaches thermowood’s, though at a price point that narrows cedar’s usual cost advantage.

For outdoor saunas exposed to weather, barrel saunas, cabin saunas, or any structure without full climate control, thermowood’s Class D durability rating makes it the more dependable long-term material. Cedar will perform adequately outdoors in moderate climates but will require more frequent inspection and maintenance to reach its full lifespan potential.

The bottom line: if you’re building a sauna you want to last a generation with minimal upkeep, thermowood is the stronger investment. If you’re comfortable with a regular maintenance routine and value the traditional cedar experience, Western Red Cedar remains a proven and widely available choice.

Frequently Asked Questions

Here are the most common questions sauna builders ask when choosing between thermowood and cedar.

What is Thermory wood?

Thermory is an Estonian wood products company and the most widely recognized thermowood brand in the sauna industry. They heat-treat pine, aspen, and spruce using the ThermoWood process, producing the Thermory aspen and Thermory spruce you’ll see specified in premium sauna kits. Thermory products meet the Finnish ThermoWood Association’s certification standards.

Does thermowood warp or crack in a sauna?

No, and that’s why thermowood is chosen over untreated wood for saunas. The heat treatment significantly reduces the wood’s equilibrium moisture content, so it absorbs and releases very little moisture during sauna heating cycles. The result is minimal swelling, shrinking, or surface checking even after years of daily use.

Can thermowood be used for outdoor saunas?

Yes. Thermowood’s low equilibrium moisture content and Class D durability rating make it well-suited for outdoor barrel and cabin saunas exposed to the elements. It handles freeze-thaw cycles and ambient humidity better than untreated wood and doesn’t require chemical preservatives to maintain that performance. Browse our range of outdoor sauna kits to see which models feature thermowood interiors.

Does thermowood smell?

Thermowood has no natural aroma. Some users add cedar accessories, such as a cedar bucket and ladle, or use essential oils to replicate the scent experience in a thermowood interior.

Is cedar or thermowood better for sauna benches?

Both work well. Thermowood aspen and alder stay cooler to the touch at high temperatures, making them preferred for bench slats where skin contact is constant. Cedar benches are comfortable, and cedar’s role in traditional saunas is well established. Many builders choose cedar for benches specifically to capture the aromatic experience where it matters most.

How often does cedar need oiling in a sauna?

For home saunas, oiling every one to two years is a reasonable baseline. Commercial settings with daily use may require more frequent attention. Skipping oiling accelerates surface checking and shortens the wood’s usable lifespan.

Can you mix thermowood and cedar in the same sauna?

Yes, and it’s a practical approach. A common configuration is thermowood for walls and ceiling cladding (where low maintenance and dimensional stability matter most) and cedar bench slats (where the aromatic benefit is most noticeable during use). If you’re shopping pre-built kits, look for models that specify Thermory aspen or Thermory spruce for the interior.

Is thermowood safe for saunas?

Yes. The heat treatment process is entirely chemical-free. No preservatives or adhesives are introduced at any stage. This makes thermowood safe for high-temperature, skin-contact environments, including bench slats and backrests. It is used in both residential and commercial sauna construction worldwide.

Choosing between cedar and thermowood involves more variables than most buyers expect. If you’d like help narrowing it down for your specific climate, build type, and budget, the team at Sauna University has additional guides, or you’re welcome to reach out directly and we’ll work through it with you.

Choosing between cedar and thermowood is a tough decision since there are a lot of things to consider. Let us show you all the factors so you choose right.