Besides ambient temperature, humidity is also an important factor affecting the thermal insulation properties. It has been reported that the thermal insulating materials from natural fibers are sensitive to moisture in the surroundings into which they are built . Nevertheless, in comparison to other natural materials (wood,wool, etc.) the moisture sensitivity of hemp, flax and jute is lower[1]. It has proved that rice straw with rich waxes on the surface can prevent water vapor from per meating into the inner layers of straw. Predictably, the moisture sensitivity of rice straw should be even lower. However, the porous inside rice straw and between rice straw particles of RSTIB will lead to moisture content changes of the boards related to humidity inevitably. The thermal conductivity coefficient is generally increasing with higher humidity. Numerous works [1,52,53]