ThermoWood^® is a patented brand created by the International ThermoWood^® Association. It specifies the natural preservation process to transform wood into a durable product.

The International ThermoWood^® Association was founded in 2000. Today, there are sixteen members from eight countries.

The ThermoWood^® trademark that specifies wood products manufactured via a process developed in Finland. Members disseminate the underlying production method to ensure the best guarantee for the quality of our various products.

Only the members of the International ThermoWood^® Association have legal right to use the word ThermoWood^® with thermally modified timber. ITWA logotype is an official quality control stamp of the association.

Kiln dried wood is not thermally modified wood. It is simply dried in a kiln to a certain moisture content to help it perform better for its final usage. Kiln drying doesn’t change the cellular structure of the wood as does thermal modification.

Thermal modification is a scientific process that changes the characteristics, chemical composition, structure and performance of wood at the cellular level. Thermally modified woods are super-heated, at much higher temperatures than kiln-dried woods, in a highly controlled manner.

No, thermal modification of wood popped up in the early 20th century when a scientific study showed how thermal modification improved the qualities of timber and enhanced its resistance to moisture. As of 2022 almost 250,000 m³ is produced annually.

Thermal modification of timber takes place in industrial-scale facilities. The ThermoWood^® process is suitable for both hardwoods and softwoods and it is always optimized for the wood species used as the raw material.

At the start of the process, timber is turned into batten bundles, which are transferred to the kiln. During thermal modification, the timber is protected by means of steam, which also influences the permanent changes that take place in the timber.

The ThermoWood^® process can be divided into three main phases.

Phase 1: High-temperature drying
The kiln is heated rapidly to 100°C. After this, the temperature is gradually increased to the desired level. During this process, the timber dries and its moisture content decreases to 2%.

Phase 2: Thermal modification
After high-temperature drying, the kiln is maintained at a steady temperature and the actual modification takes place.

Phase 3: Cooling/conditioning
During the last phase, the temperature in the kiln is decreased with a water-spray system. When the temperature is sufficiently low, the timber’s moisture content is increased using water and steam to improve its machinability and dimensional stability. After the cooling phase, the moisture content of ThermoWood^® products is 4 to 7%.

No, ThermoWood^® is a wood material produced by using only natural elements: heat and steam. Thermal modification improves the wood’s technical properties and ThermoWood^® is non-toxic, dimensionally stable, resistant to decay and resin free. It can be used inside or outdoors, in any climate.

Genuine ThermoWood^® exists in two standard treatment classes, Thermo-S and Thermo-D.

The letter 'S' in 'Thermo-S' stands for 'stability'. Along with appearance, stability is a key property in the end use applications of the products in this treatment class.

The letter 'D' in 'Thermo-D' stands for 'durability'. Along with appearance, biological durability is a key property in the end use applications of products in this treatment class.

At LDCwood^® the standard is Thermo-D which is the highest classification, suitable for exterior cladding and decking applications, as well as interior applications.

Through every fiber, the durability class improves from IV or III up to I and II which implies a lifespan of over 25 years for class I (EN 350-1).

The thermal modification process gives ThermoWood^® a distinctive brown coloring. However, the brown color will start to fade over time due to the effect of the weather conditions. As it does, the wood will begin to turn grey gradually. The color can vary from a platinum silver to a lighter rustic tone depending on the construction and the climate conditions it has been exposed to.

Keep in mind that wood is a natural material and so any color changes may be uneven. Each board ages in its own way and different sides of the building’s facade will also age differently depending on the sun and rain they’re exposed to.