Thermoforming describes the production of three dimensional structures from flat sheet. In general, it is used for the production of simple shaped packaging or housing parts without any additional functions. However, by the use of heat conductive plastic sheets, additional functions can be implemented to the thermoformed parts, e.g. heat management function in housings. Heat conductive plastic materials are plastics filled with thermally conductive fillers. The more filler is applied, the better is the compound’s heat conduction. The heat conduction does not only depend on the filler content, but also on filler geometry as well as filler orientation. Furthermore the fillers (content, geometry, orientation) influence the stretching behavior of a sheet. In this investigation the influence of filler geometry (plate-like, spherical) and filler content (0, 5, 10, 15, 25 vol.%) on the stretching behavior of polystyrene is determined. Furthermore, the influence of stretching on filler orientation as well as heat conductivity is examined. The thermoformability is analyzed by the IKT Thermoforming-material-characterization test. The influence of stretching on thermal conductivity is determined by combined tensile tests and laser flash analysis. Finally, the combination of both effects is characterized by thermoforming ex-periments.