This thermal modification process uses oil a treatment medium where immersion of air-dried or kiln dried bamboo poles are performed. Poles are exposed in hot oil at a desired temperature level (usually above 160°C). Depending on the target exposure time, duration of treatment starts when the oil reached desired temperature (±5°C). Thermally modified poles are removed from the oil bath  once the temperature is below 50°C.  TM bamboo poles are conditioned for a week or so before utilizing as a material to assemble BMIs.

Physically, thermal modification produces poles with a darker color. While altering its acoustic properties, chemical changes in the bamboo due to hot oil treatment makes it less capable to absorb moisture, less susceptible to biological attacks, with a slightly weakened strength properties (depending on the severity of temperature exposure).

Both TM in steam and oil can change the color of the bamboo poles as shown in the photo.