Genuine ThermoWood has two standard treatment classes, Thermo-S and Thermo-D. Having more than two classes is not reasonable since wood properties change slowly at first as the temperature increases. Once the treatment temperature exceeds 200 °C, the properties change rapidly. 

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.


ThermoWood is a product which is manufactured using a special high temperature kilning process which has been developed in Finland. ThermoWood not only protects the timber with a high heat and steam process but also brings up some chemical changes as well.


ThermoWood is the brand which is allowed to be used only by the member of The International ThermoWood Association. With the ThermoWood Process the sugar inside the timber gets caramelized and that causes the colour change, making the timber more stable and durable compared to regular Kiln Dried timber. Thanks to the thermal modification, the swelling and bending range of the timber has been minimised.

The heat treatment process is made up of several phases and is divided into six different sections in which the treatment occurs very slowly. The total treatment time lasts up to 100 hours. In every section a different treatment is done, each individually monitored and controlled and done in parallel with the other sections, transition between sections is done seamlessly and without interruption. It is in the fourth section tha the actual heat treatment occurs, the sections prior prepare the material and the sections that come after are important to stabilise the material afterwards. With this system it is possible to treat large amounts without the material having to undergo "stress" and start to crack.


A hot tub made of special quality heat treated wood (used by SpaDealers) is not sensitive to dry weather. This is because the material is already so dry during assembly that it won't shrink any more. However, it can still expand a little and tighten any small leakages that may occur during the first time of use. Therefore no water needs to be kept in the hot tub in order to prevent leakages. As a result, maintenance is much easier and water hygiene is better. The weight of heat treated wood is also much less. There is no resin left and the insulation effect is 30% better.


During the ThermoWood Process the biological durability of ThermoWood products are being increased due to the hemicellulose breakdown. As these are the nutrients of the bacteria causing decay and fungus which are pulled out during the ThermoWood process.

ThermoWood products have a durability against various types of fungus as well as being durable against wood destroying basidiomycetes.

The ThermoWood process does not protect the materials from algee and fungus on the surface. These organisms feed from the environment and does not cause and structural changes on ThermoWood products. The algee on the surface which can be seen as an aesthetic clause and can be easily prevented with the surface treatment (Such as wood preservative oil, water-based varnish).


The main properties and advantages of Lunawood thermowood:


  • Resin-free: the resin dries or evaporates completely;
  • Weather resistant;
  • During the heat treatment, the color of the wood changes and dark brown, noble tones are created. It should be noted that the color change is continuous (extends over the entire thickness), which is clearly visible on the cut;
  • The thermal conductivity (insulation capacity) of wood is in the range of 0-30%. Reduced thermal conductivity is another plus of thermowood. Compared to ordinary wood, the thermal conductivity is 20-25% lower;
  • The surface strength of Thermowood increases. Compared to ordinary wood, the strength of the surface layer increases by 5-20%;
  • The ability to absorb moisture decreases. First, it is the stability of the geometric dimensions in the event of strong exposure to moisture and temperature changes. Simply put, when water gets on the product, it doesn't deform, swell and dry out. Thermowood absorbs 5 times less moisture than ordinary wood because its surface is dense and non-porous and its capillary structure is also changed. But even if the thermowood has absorbed a little moisture, it does not change its size and remains as it was when dry;
  • Non-toxic. Lunawood thermowood is completely natural and contains no chemical additives. Thermowood is made using a natural process using heat and steam.
  • Increasing the bacteriological resistance of wood. The Finnish thermowood Lunawood is "inedible" for various fungi, insects and other pests. During the heat treatment, wood sugar decomposes, a nutrient medium for microorganisms that contribute to the decay of a wood;
  • The durability of Finnish thermo wood increases.