Thermal treatment of beech wood at 200°C for different durations affects the surface quality of the wood. Longer treatment times result in rougher surfaces, with vessel cavities becoming deeper and ray tissue showing more fiber pull-out and plasticization. The roughness parameter Rk is the most accurate measure of surface quality, while Ra may not fully capture the changes. Thermal treatment reduces surface waviness, and using roughness parameters is essential for accurately assessing surface differences.