Thermally modified timber is wood that has undergone a heat treatment procedure to reduce the moisture content, and increase it's resistance to decay by destroying fungi. It's is widely used throughout the carpentry and construction industry. This procedure can have some undesirable side effects on tonewoods used to build musical instruments, such as decreasing elasticity, bending strength, as well as changing the color.
Tampere University of Technology, Luthiery department of Ikaalinen School of Arts and Crafts, and a company named Suomen Ekopuu, have worked together to developed a special heat treatment procedure which is suitable for tonewoods. This procedure was developed with extensive scientific research utilizing a large number of guitars, and guitar parts at a Finnish guitar factory.
The procedure doesn’t have so much in common with ”roasted maple”, "torrefied wood”, or other common trade names widely sold today, they’re all more or less violent to woods flexibility. This special procedure achieves the same effect on the woods cellular structure that naturally happens after slowly drying for 15 years - but without any of the unwanted effects caused when treated with higher temperatures. As a result, this wood has increased stability and speed of sound, but still has the flexibility to produce great projection, which makes it an ideal choice for top wood. The colour changes only as much as the wood colour would naturally change over 15-20 years. New guitars made with Thermo Wood treated tops sound more mature and sensitive like an old guitar.