This procedure called “thermal modification” decreases water absorption in wood, thus increasing its resistance to decay while reducing swelling and shrinking. Another factor that contributes to wood’s exceptional durability is the crystallization of cellulose. The modification of hemicellulose enhances its durability, where hemicellulose is broken down into furfural and carboxylic acid. Additionally, the application of heat causes lignin to caramelize, resulting in a darker color.

A method in which the chemical properties of wood are modified with heat and steam. The minimum modification temperature is 160°C. The consequent changes in the wood structure are permanent.

The modification phases are high-temperature drying, thermal modification and cooling, and moisture conditioning. The process results in permanent physical and chemical changes in the wood. The new properties remain unchanged, even when the timber is processed with methods such as sawing or planing. 

• Drying: Using heat, the oven temperature is raised to 100⁰C quickly. Then, the temperature is constantly raised to 130⁰C, during this time the wood is dried and the moisture is reduced to zero.
• Heat treatment: The temperature in the wood is increased to 180⁰C (Thermo S) and 212⁰C (Thermo D) with water vapor. When the target temperature is reached, this heating process is applied for 2-3 hours.
• Cooling and humidification: In this last part, the temperature of the wood is lowered to 80⁰C – 90⁰C by the use of the water spray and it is continued until the humidity of the wood reaches 4–6%.

Heat treatment increases the stability and durability of wood. Wood is composed of 50% cellulose, 23% hemicellulose, 20% lignin, and 7% other organic compounds, called extractives. Heat treatment eliminates resin, all other extractives and bonding water called OH (Hydroxil) groups from the wood. This process reduces water absorption of wood, consequently increasing decay resistance while decreasing swelling and shrinking. Another factor that contributes to the high durability of wood is the crystallization of cellulose. The change in hemicellulose increases the durability. Hemicellulose is separated into furfural and carboxylic acid. Caramelization of lignin, caused by heat, results in a darker color appearance of the wood.

Thermally treated boards undergo natural aging and develop a gray patina over time, unless preventive measures are taken. Therefore, the initial consideration is whether to preserve the boards’ original color or embrace their natural aging process.

No chemicals are used in the production of Thermally treated wood. All raw materials are procured from certified sources. The production method is a result of extensive development work and it is based on the controlled modification of timber with heat, steam and water.

Thermally treated wood is lightweight and easy to install. For that reason, it is ideal for projects where extra loading on the building is a concern.