Abstract: A nonlinear parameter estimation method was adopted to determine the thermal diffusivity of a xonotlite-type calcium silicate insulation material. The measurements were performed with a laser-flash apparatus by rear-face detection of the temperature response of the three-layered sample, where the insulating material was sandwiched between two iron slices. The thermal diffusivity was evaluated by fitting the theoretical curve with the recorded temperature-time one. The nonlinear parameter estimation technique can simultaneously estimate the thermal conductivity, heat transfer coefficient and absorbed energy. Based on experimental results, the optimal thickness range of the insulation material in the sample was suggested from 1.6 to 1.9 mm. The effect of thickness and contact resistance on measurement uncertainty was estimated within 5.8%