Thermal modification of wood involves heating wood material to a temperature of at least 180ºC while at the same time protecting it with steam. The steam protects the wood, but it also influences the chemical changes taking place in wood. Thermal modification involves using heat and water vapour to produce environmentally-friendly modified (wood) products, which are free of any impregnation substances.
Thermal modification impacts on several wood properties changing them permanently. The dimensional stability of wood significantly improves in conditions where the moisture level varies. Also, the thermal insulation properties of wood thus treated are superior to those of non-treated wood. The effect of treatment applied at a sufficiently high temperature is such that wood becomes decay-resistant. Thermal modification does cause a slight reduction in the strength properties of wood. Thermal modification can be successfully applied to the wood of nearly all tree species. The lovely shades of colours produced by heat treatment can be preserved by applying oil or pigments to the wood surface.