In this investigation, a new thermal insulation material (RSTIB) from rice straws with a low density of 200–350 kg/m3, a thickness of 40 mm and the thermal conductivity of 0.051–0.053 W/(m K) was developed using high frequency hot-pressing. It could be used as a component of construction material as wall or ceiling insulation for energy conservation. Thermal conductivity was found to be correlated with the boards’ density and ambient temperature. Additionally, the thermal conductivity increased with decreasing particle size, and the results showed that the particle MC