What is the history behind thermally modified wood?
Posted: June 7, 2026Author – Ryan Palma Owner/CEO Sustainable Lumber Co.
We have officially launched our new line of thermally modified wood siding Montanafied! Currently available in 1×6 and 1×8 T&G smooth and wire brushed texture. Call or email us for more information and pricing, info @ sustainablelumberco.com or (406) 642-7120
The History of Thermally Modified Wood Products
Thermally modified wood is one of the hottest trends in sustainable building right now, and for good reason. It delivers exceptional stability, natural durability, and beautiful color without any chemicals. But while it feels like a modern innovation, its story stretches back much further than most people realize.
After a year of research and development our new thermally modified spruce siding is a perfect fit for Montana’s harsh and demanding climate. Understanding where it came from helps explain why it performs so well today.
Ancient Roots: Fire as a Wood Preservative
Long before laboratories and patents, people discovered that heat could make wood tougher.
Vikings charred the timbers of their ships to help them withstand harsh sea conditions. Ancient civilizations used similar techniques to protect wood from moisture and decay.
The most famous traditional method is Japanese Shou Sugi Ban (also called yakisugi). Artisans carefully char the surface of cedar boards, creating a striking black finish that resists rot, insects, and fire. This beautiful technique is still used today on high end homes and gives us a glimpse into the long relationship with heat treated wood.
The Scientific Spark
The modern story of thermally modified wood begins in a laboratory. In 1915, Harry Tiemann, a kiln specialist at the U.S. Forest Products Laboratory in Madison, Wisconsin, conducted the first documented scientific experiments. He heated wood in superheated steam and observed that it became significantly less likely to absorb moisture.
Over the following decades, researchers in Europe and the United States continued studying heat treatment. However, most of this work stayed in the lab. Challenges like inconsistent results, strength loss, and the lack of scalable equipment kept it from becoming a practical commercial product.
The Real Breakthrough: Finland in the 1990s
Everything changed in the early 1990s in Finland.
The VTT Technical Research Centre of Finland, working with the Finnish wood industry, developed the first true industrial scale process for thermally modifying wood. They perfected a method of heating wood to high temperatures (typically 350-500°F) in a controlled, low oxygen environment using steam. This process chemically alters the wood throughout, breaking down sugars that attract mold and insects while dramatically improving dimensional stability.
In 1994, VTT patented the process and registered the ThermoWood® trademark. Commercial production began in the late 1990s, and the Finnish ThermoWood Association (now the International ThermoWood Association) was formed around 2000 to set quality standards and spread the technology across Europe.
This was the moment thermally modified wood went from interesting science experiment to reliable, high performance building material.
Coming to North America
While Europe embraced the technology in the early 2000s, it took a bit longer to reach the U.S. The first industrial scale production in North America began around 2007. Since then, demand has grown steadily as builders and homeowners look for sustainable, chemical free alternatives to tropical hardwoods and pressure treated lumber.
Today, thermally modified wood is used for siding, decking, cladding, and interior applications across the country, and it’s gaining serious traction in places with extreme weather, like Montana.
Why This History Matters for Montana
Montana’s climate is tough on wood. Freeze thaw cycles, intense sun, wind, and moisture swings can cause ordinary wood to warp, crack, and decay quickly. Thermally modified wood was literally engineered to solve these problems:
- Up to 50%+ less moisture absorption
- Significantly better dimensional stability
- Natural resistance to rot and insects
- Beautiful, rich color that develops through the entire board
- 100% chemical free process
By sourcing locally grown wood and modifying it here in Montana, we can offer builders and homeowners a high performance product at a lower cost, with a dramatically lower carbon footprint than imported options.
The Bottom Line
Thermally modified wood isn’t brand new, but the refined, consistent, industrial version we have today is the result of over 100 years of scientific curiosity and a breakthrough in Finland just 25–30 years ago. It combines ancient wisdom about heat and wood with modern precision engineering.
At Sustainable Lumber Co., we see it as a natural evolution of what we’ve always done: offering beautiful, high quality, sustainable wood products that perform in the real world, right here in Montana.
Contact us for a quote
Our knowledgeable team at sustainable lumber is here to answer any additional questions you may have. Call us today for a free quote (406) 642-7120 or click here to submit an inquiry online. We look forward to helping you with your next project!