Functionalized polymers are gaining increasing importance and are replacing metallic materials in various areas. Unlike metals, they are stable to a wide variety of chemically aggressive fluids. There are several filler materials that increase the thermal conductivity of polymers, e.g. carbon based such as graphite, CNTs and graphene but also ceramics like boron nitride and aluminosilicate. For the heat management in HT-PEM fuel cells it is very important to know the thermal conductivity and the thermal transfer coefficients. There are different methods to determine thermal conductivity of polymers that are described in DIN EN ISO 22007-1 “Determination of thermal conductivity and thermal diffusivity”, which work with different physical methods to maintain the thermal conductivity. Actual investigations within a BMVi Project (BePPel) at ZBT lead to different conductivity values using different measurement methods. These differences, which should not be neglected, complicate the design of a HT-PEM fuel cell. This poster describes the differences in measuring systems flash-method (LFA457), transient plane method (HotDisk 2500S) and modified transient plane method (C-Therm TCi) and compares their informative value. Models found in literature to calculate the thermal conductivity and simulations are used for comparison.