A technique is presented for measuring the thermal diffusivity of solids. This technique differs from others in that boundary conditions are obtained by use of a well‐stirred constant‐temperature bath. By varying the bath temperature and the initial temperature of the specimen, thermal diffusivity values may be determined as a function of temperature. Accuracies within ±5% may be obtained and the major sources of error in the technique may be isolated and controlled. The method lends itself to remote‐control testing of hazardous materials such as high explosives and solid propellants. In the present studies thermal diffusivities ranging from 0.005 to 0.010 ft2/h were measured between −65 and 165°F on a typical high explosive material.