Thermal modification (TM) in a steam environment can be used to treat air-dried or kiln dried bamboo poles. The TM may be performed in a cylindrical steam chamber or in a typical kiln-drying chamber fitted with heaters to raise the temperature above 160°C. Poles were exposed in a boiler-produced steam at a desired temperature level. Depending on the target exposure time, duration of treatment starts when the desired temperature (±5°C) is obtained. Thermally modified poles are removed once the built-up pressure within the chamber depleted, and 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 steam 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).