A new and rather simple apparatus is described for measuring the thermal conductivity of insulating materials. The technique employs a double-sided, copper-coated plastic sheet, known as a printed circuit board, to generate a nearly uniform wall heat flux. Heating is achieved by passing an electrical current through the copper coating. Identical sample slabs are placed against opposite sides of the heater, and the combination is placed in a bath having constant and uniform temperature. When thermal equilibrium is reached, the temperature drops across the central portions of the sample slabs are measured with thermocouples. The one-dimensional form of Fourier heat transfer equation is used to compute thermal conductivity from the observed quantities. In preliminary tests with polymer materials, equilibrium is reached within half an hour. It is estimated that the apparatus is capable of giving measurements accurate to within 5%, and experimental results are consistent with this estimate. Thermal conductivity values are reported for pure polyethylene (PE) and PE mixed with aluminum powder and carbon black. Also reported is the thermal conductivity of pure polycarbonate (PC) and PC mixed with carbon black. The results obtained with the present apparatus are consistent with previous findings. The characteristics of the apparatus make it especially suitable for academic laboratory instruction and for low temperature thermal conductivity measurements. (C) 2003 Wiley Periodicals, Inc.