Thermal Modification of Wood

Thermal modification is a process in which wood is treated with only heat and steam—without any chemicals—enhancing its stability, durability, and resistance to decay.

In our mills in Finland, the ThermoWood® process raises the temperature inside the chamber to 212°C (413°F), with the entire treatment lasting up to 110 hours. Water is used to prevent the wood from burning and cracking at high temperatures and to ensure the final product’s excellent technical qualities. During the process the molecyl structure of the wood changes and sugars are removed from the wood, that may lead to rot.  The result is an exceptionally stable and weather-resistant wood material with a uniform brown color and a moisture content of just 4–7%, making it ideal for both exterior and interior applications. The expected lifespan of Lunawood ThermoWood® cladding is over 25 years (Source: BRE).

The technology we use in the US follows the same natural and controlled process of treating wood to enhance its durability and longevity.

After the modification process is complete, we plane the wood into various Lunawood Collection products, designed to meet the needs of modern architecture and construction.

While our Finnish production relies on PEFC-certified Nordic Pine and Spruce—sourced from sustainably managed forests near our mills—our U.S. manufacturing in Georgia utilizes local hardwood species such as Yellow Poplar and White Ash. Both options are available with FSC certification upon request, ensuring transparency in wood sourcing. By relying on renewable and well-managed wood materials and a chemical-free process, we are proud to provide genuinely sustainable wood products.

Lunawood has set the highest standard in thermal modification of wood since 2001. Each Lunawood products is a result of decades of expertise, continuous research, and a commitment to sustainability. The patented ThermoWood® process is audited three times a year by an independent external auditor. Our in-house laboratories in Finland and USA conduct rigorous testing on every production batch—both after the modification process and after planing.