An experimental system to determine the anisotropy ratio of thermal conductivity of polymer foils parallel to the sample surface is presented. This kind of measurement is important because the drawing of the foil orients the molecular chains making thermal conductivity parallel to the orientation higher than perpendicular to it. The measurement method is based on heating the foil with a dc‐supplied resistor and detecting the temperature by an infrared detector. The temperature of the foil is measured as a function of distance from the heat source in two separate measurements perpendicular to each other, i.e., rotating the sample 90° between the measurements, and the anisotropy ratio of thermal conductivities in these directions is obtained by using curve fitting. In this article the method has been applied on several plastic foils showing anisotropies ranging from 1 to 2.