This article describes an experimental technique to measure simultaneously the thermal diffusivity and thermal conductivity of nonmetallic materials. The method is applied to a large thickness sample and uses a single temperature sensor located at the heating surface of a perspex sample. In addition the golden section optimization technique is used with parameter estimation for minimizing two different objective functions. Each of the thermal properties is estimated in a different way. The diffusivity estimation uses a correlation function estimator between heat flux and temperature while a square function error of experimental and estimated temperatures is the objective function used for determining the conductivity. A comparison with the guarded hot plate method indicates a deviation of 2.1&percent; of the thermal conductivity. An error analysis for both properties is also presented. ©1998 American Institute of Physics.