The thermal conductivity of materials that are poor conductors of heat is usually determined by measuring the larger temperature gradients in the sample produced by a steady flow of heat in one-dimensional geometry. In order to reduce the errors of radiation and convection, it often requires large, precisely shaped samples and extreme care to be used successfully. This international standard specifies a modulated temperature method realizing the measurement of thermal conductivity. An input of temperature deviation is less than 1 K, and a double lock-in method is applied to amplify the small temperature modulation. The ISO22007-3 specifies one of the modulated temperature methods where the phase shift is measured in the thermally thick condition kd >>1 (k=(wð/2að)1/2, wð: angular frequency of temperature wave, að thermal diffusivity, d: thickness of the specimen). In this condition, the backing material does not affect on the phase shift results on the sensor, on which temperature wave decays exponentially. On the other hand, if kd << 1, the decay of temperature modulation is influenced by the backing materials. Based on this principle, this standard specifies the method to determine the thermal conductivity of the sample (as a backing material), comparing the decay of temperature wave detected on both surfaces of the probe material. Thermal conductivity is determined from the correlation between the thermal impedance and the decay ratio of amplitude using two reference materials measured at the same frequency and temperature. For instance, if water and air are chosen for reference materials, thermal conductivity is determined in the range from 0,026 W/mK to 0,6 W/mK. The covering range is adjusted with the reference materials and the probe materials.