The Thermal Modification process enhances wood’s properties from to end to end. The entailed wood is treated with steam and heat only, no chemicals are used at any stage of the process.
The temperature inside the thermal modification chamber is slowly raised to 212°C and the whole process can last up to 110 hours. Water is needed for two reasons: because the temperature rises so high, the water prevents the wood from burning during the thermo-treatment process. Water is also used to ensure the high quality of the final product. At the end of the process, moisture is added to the chamber to prevent cracking and ensures a long life for the final product. When the process is complete, the moisture percentage of the wood is around 4–7%, which makes Thermowood products extremely stable and durable.

The Thermowood process was patented and the Thermowood® trademark was launched in Finland at the end of the 1990s. The production process is audited three times a year by an external auditor. In addition, we carry out continuous quality control ourselves, as we take 10 samples of each furnace load and test them in our own laboratories in Iisalmi and Kaskinen. These test results are audited a couple of times a year by an external auditor.