THERMALLY MODIFIED WOOD AND YOUR SAUNA
Thermally modified wood isn’t new—but the way it’s used in modern saunas has evolved dramatically. What began centuries ago as a way to strengthen ship hulls and structural posts is now a refined, oxygen-controlled heat treatment process that transforms wood at a cellular level.
In this guide, we’ll break down:
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What thermally modified wood actually is
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How the heat-treatment process works
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Why it improves durability and moisture resistance
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How leading sauna brands use thermowood in real-world indoor and outdoor models
By the end, you’ll understand whether thermally modified wood is the right choice for your sauna—and what to look for when comparing barrel, cabin, and cube-style designs.
What is Thermally Modified Wood?
Thermally modified wood is lumber that has been heat-treated in a controlled, low-oxygen environment to permanently alter its cellular structure. During this process, the wood is heated to approximately 356°F (180°C) or higher, removing moisture and changing the chemical composition of the wood fibers.
The absence of oxygen is key. Without oxygen, the wood doesn’t burn—instead, it undergoes structural changes that improve:
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Dimensional stability
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Moisture resistance
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Biological durability
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Long-term performance in changing climates
Some manufacturers incorporate steam during the heating cycle, while others may use oils or chemical additives. For sauna applications, the most desirable thermally modified woods are treated using only heat and water vapor—preserving the wood’s natural character without introducing synthetic preservatives.
Today, brands like Forever Saunas, SaunaLife, and Auroom, use thermally modified spruce and aspen to create sauna structures that are both durable and visually refined.
How Is Wood Thermally Modified?
Thermally modified wood is produced in a controlled heating chamber where lumber is gradually heated in a low-oxygen environment. This removes moisture and permanently alters the wood’s cellular structure—without relying on chemical treatments.
For outdoor sauna applications, higher temperatures are used to increase durability and resistance to rot. After peak heating, the wood is carefully cooled and reconditioned to stabilize it for long-term use.
The result is wood that is more dimensionally stable, less prone to swelling, and better suited for repeated high-heat, high-moisture conditions.
What Are the Benefits of Thermally Modified Wood?
Thermal modification enhances wood from the inside out, improving performance without chemical preservatives. For sauna construction, the benefits are especially meaningful.
1. Increased Durability Heat treatment strengthens the wood throughout—not just the surface—making it more resilient in outdoor environments.
2. Improved Dimensional Stability Thermally modified wood absorbs less moisture, meaning it expands and contracts significantly less. This reduces warping, twisting, and cracking during sauna heat cycles.
3. Enhanced Bio-Resistance The altered nutrient structure makes the wood less hospitable to fungi, pests, and microorganisms—without toxic additives.
4. Better Insulating Properties Independent testing suggests thermally modified wood can offer improved thermal insulation compared to untreated lumber, helping retain heat efficiently inside a sauna.
5. Lighter Weight The process reduces density slightly, making installation easier while maintaining structural integrity.
6. Rich, Refined Appearance Heat treatment deepens natural color and enhances grain patterns, giving thermowood a warm, premium aesthetic.
7. Chemical-Free and Eco-Conscious When modified using only heat and steam, thermowood remains free of synthetic preservatives—making it ideal for interior sauna environments.
Explore Thermally Modified Wood Sauna Models
If you're considering a sauna built with thermally modified wood, here are a few standout examples:
Forever Saunas Barrel Collection (Outdoor)
Crafted from thermally treated spruce and designed for backyard installations, Forever barrel saunas combine durability with elegant design. Available in 2–6-person sizes, with glass-front options and premium HUUM heater compatibility.
Auroom Cala & Libera Cabin Saunas (Indoor Thermo-Aspen)
These Scandinavian-designed indoor cabins feature satin-smooth Thermo-Aspen interiors for dimensional stability and refined aesthetics—ideal for homeowners prioritizing craftsmanship and long-term performance.
Is Thermally Modified Wood Recommended for Saunas?
Yes—thermally modified wood is exceptionally well-suited for sauna construction, especially in outdoor environments.
Because the heat-treatment process reduces moisture absorption and improves dimensional stability, thermowood performs reliably under repeated heat cycles and humidity swings.
It also enhances the performance of common sauna woods:
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Pine: Typically prone to warping, but significantly more stable when thermally modified.
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Nordic (European) Spruce: Naturally attractive and aromatic, with reduced risk of sap seepage after heat treatment.
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Aspen: Becomes even more dimensionally stable and refined in appearance when thermally treated.
The result is wood that expands and contracts less, resists rot more effectively, and maintains structural integrity in both indoor and outdoor sauna installations.
Indoor vs. Outdoor Thermally Modified Sauna Options
Thermally modified wood performs exceptionally well in both environments—but the right model depends on your installation goals.
Outdoor Barrel & Cube Models
Forever Saunas and SaunaLife models use thermally modified spruce and aspen to withstand snow, rain, and seasonal humidity shifts.
For modern outdoor design with architectural glass and premium finishes, models like the SaunaLife Cube Series and Auroom Mira offer a contemporary take on thermowood construction.
Indoor Cabin Saunas
Auroom’s Thermo-Aspen interiors offer dimensional stability with a lighter, refined finish ideal for home wellness rooms.
What Can You Expect From Today’s Thermally Modified Sauna Collections?
Thermally modified wood has evolved—and so have the sauna brands using it. Today’s leading manufacturers combine advanced heat-treatment processes with refined design, ergonomic engineering, and high-performance heater systems.
At My Sauna World, we curate thermowood saunas from brands that approach craftsmanship differently—so you can choose the style, configuration, and feature set that fits your space.
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Forever Saunas – Outdoor Barrel Performance with Strong Value
Built from thermally modified Nordic spruce, Forever barrel saunas promote efficient heat circulation and offer shingle roofing, glass-front options, and compatibility with HUUM or Harvia heaters for rich, long-lasting steam.
👉 Explore Forever Thermally Modified Barrel Saunas
Auroom – Scandinavian Craftsmanship with Thermo-Aspen Interiors
Auroom combines Thermo-Aspen interiors with architectural-grade glass and UV-protected exteriors. Their models are ideal for homeowners seeking premium materials and modern design.
👉 View Auroom Thermo-Aspen Sauna Models
SaunaLife – Modern Thermowood Barrel & Cube Designs
SaunaLife blends thermally modified construction with Scandinavian aesthetics, contoured seating, and optional Wi-Fi lighting integration for a refined, contemporary sauna experience.
👉 Discover SaunaLife Thermowood Saunas
Why Thermally Modified Wood Continues to Lead
Across all three brands, thermowood delivers consistent advantages:
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Improved dimensional stability
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Reduced moisture absorption
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Enhanced bio-resistance without chemicals
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Long-term durability in outdoor climates
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Rich, elegant color tones
Whether you’re building an indoor wellness space or installing a backyard sauna retreat, thermowood provides a strong foundation for performance and longevity.
Ready to Find the Right Thermowood Sauna?
If you’re exploring thermally modified wood for your next sauna, our team is happy to help you compare models, installation requirements, and heater options. We curate our collection carefully so you can shop confidently—knowing each model meets our standards for durability, design, and long-term value.
👉 Browse All Thermally Modified Wood Saunas
Have questions about sizing, climate durability, or heater compatibility? Reach out anytime—we love talking sauna.
Let customers speak for us
I haven't even built this sauna yet (Rainelle), but I have to give an ENORMOUS shoutout to Adora and especially KELLY for their help on this one. This was a big purchase for us, and these ladies went way out of their way to make it work out for us. The first sauna that showed up was badly damaged in shipping, and from what it sounds like - that is not typical. At all. So Kelly helped us to get it squared away, and it took what could have been a horrible customer experience into a fantastic one. Give this woman a raise!
We really like our sauna! Quality of the sauna seems decent. The quality of the accessories was not! The back recliner was all busted up out of the box.
My wife and I would occasionally sit in the sauna at our gym after a workout. It was hot but a little gross. I can't tell you how many times we bailed on the gym sauna session because someone else was playing their phone too loud, someone was breathing like they were gasping for air, someone decided to be shirtless in public, someone is weird or any number of other reasons. Loved the sauna feeling but HATED the gym sauna.
We bought a sauna for our home and installed it in our basement to escape the gym sauna experience. We absolutely love it! We sauna daily. Without the angst and frustration of hoping to avoid an awkward gross experience at the gym sauna.
If you are considering a sauna purchase, spend a little extra and get the WIFI enabled heater. This is the best way to make sure you get the benefit of owning a sauna. The app on our phone is easy to use. Just click the on/off button on the app and set your temperature to your desire. I like 171. My wife likes 153. Once it hits the temperature, the app will let you know. You can even turn on your sauna while you are on the way home from the gym. The WIFI version and the app make all the difference in usability and enjoyment of your investment. If we did not have the app and the WIFI version, we probably would probably skip 2/3 of the sessions we currently take.
The sauna is well made. Wood quality is excellent. Very few knots and blemishes. Hillsboro Almost Heaven saunas are a great choice for quality components, solid electronics, easy to use controls and an enjoyable sauna experience.
This is a standard kit sauna. I made several modifications but I am very satisfied with it so far. I have a few shingles left to install tomorrow and then will move onto to interior. MSW has been easy to work with and I recommend them.
I really love this sauna. I use it about four times a week to help me wind down before bed and calm my ego. Customer service at MySaunaWorld was great.
Assembly took me roughly 8–10 hours total over two days, and I’m not a particularly handy person. The step by step instructions video was straightforward and easy to follow.
I paired the sauna with the HUUM Drop 9 heater (the largest HUUM Drop), and it performs very well. I hired an electrician to install it (about $900 extra). It easily heats the sauna to 190°F plus. I personally like it around 180°F, which it reaches in about an hour. Also, you can pour water over the hot rocks to make the air hotter and steamier. Make sure to mount it low so that it can heat everything above it. (I mounted mine 6” from the ground to the base of the heater.) I love that I can start heating the sauna from my iPhone, even when I’m not on my home Wi-Fi.
I got the double-bench configuration going across the back of the sauna which lets two people lay down. The area around the lower bench is cooler which is nice to have different temperature seating options.
The sauna looks fantastic, smells great, and feels solid. I would recommend this sauna to a friend.
We love our new Almost Heaven Pinnacle barrel sauna!
Delivery was perfect, the assembly was a breeze, and the sauna fits perfectly in our space.
The only regret we have is not to have made this purchase 10 years ago!
I had been thinking about installing a sauna for quite some time. I kept going back and forth between framing one in or a prefab that I assemble. I spent several weeks going over the various websites looking at designs for both and writing out the pros/cons for each. After much deliberation, I reached out to My Sauna World to purchase an Almost Heaven Greyson.
It came way sooner than expected which was a good thing, so I had to arrange for my electrician. I assembled it very easily, with my wife holding just one panel, and then I ran into a problem. The last wall was short. It took a lot of head scratching and measuring and remeasuring as well as back and forth communication with both My Sauna World and Almost Heaven. It turned out that I had been sent 2 glass panels that were the same dimension when the 2 glass panels are actually designed with different dimensions. The new panel was sent out without question, and the rest of the assembly went easy.
I will say that the folks at My Sauna World were extremely responsive and did a great job as liaison back to the manufacturer.
Overall, I had a really positive experience, and we are very happy with the Greyson with the Harvia Spirit 8kW stove.
We also have the duckboard flooring (that is a must) sitting on top of the concrete floor. The back and leg rest are also recommended.
Note: this is advertised as a 3-4 person but in reality it is a good 2 person. And lastly, I grew up with sauna my whole life, starting with my grandpa’s wood burning sauna. This non insulated Greyson type will not get up to the same temperatures, but it does get the job done. Very pleased with the product and do recommend (to frame one in my self and buy a pre-cut kit would have cost a few thousand more overall)
Their customer service is refreshing in a world where most companies fail miserably with service. They should teach customer service to other companies and government agencies. We have only tested the actual product to make sure it works, but along the way, we had multiple questions and the replies were quick and helpful. The sauna was easy to assemble.
Frankly, I was stunned at the quality of this product. Equally stunning is how easily everything fits together. It’s well and I’m looking to an improved lifestyle.
Back rests are a nice size and fit perfectly in my Lugano 3-person sauna. They are very comfortable (especially considering they are wood) and make sitting in the sauna an even more pleasant experience. To think that they were added in free to my purchase of the sauna is hard to believe. Very pleased with customer service from My Sauna World.com !
Well built, good quality, reliable, and matches my barrel sauna very well
I purchased this since it was significantly more affordable than from the brands website. It arrived quickly and is function perfect. It's easy to install and looks great. I had issues with water leaking into the sauna before that used to annoy me. Now it stays completely dry and the wood also is protected from damage and weathering.
The best Sauna ever, and the quickest delivery, 100% recommend !!!!
Works exactly as advertised. Easy install and perfect coverage. Highly recommend.
Very good customer service. My sauna came as expected.