The use of different polymers is gaining increasingly more room also in the areas that have been before dominated by metals. This progress sets more demands on the physical characterization of new plastic materials and products. Plastics have already been widely used because of their excellent insulating properties but unfortunately there has been a lack of fast, simple, and accurate methods to determine their thermal conductivity, especially when the samples are not in cast form but thin foils. In many cases it is important to determine the thermal conductivity of anisotropic samples. Drawing of polymer foils changes the orientation of polymer chains and thus affects the thermal conductivity causing anisotropy. The ratio of anisotropy depends on the drawing ratio and the structure of the molecules. The conductivity perpendicular to the foil surface can be measured with flash methods [1] but measurements in other directions are more difficult [2,3,4].