In the research project “Development of a latent heat storage system with innovative PCM modules for the application in small and middle heat and power plants” an innovative heat storage system is to be developed. Modules with integrated phase change materials (PCM) shall be integrated into a heat storage system to make latent heat usable. Regarding this, the novel heat storage system presents an optimization towards conventional sensitive heat storage systems. One subsection of this research project is the development of an extrusion line for the inline inflation of extruded circular pipes with PCM. To design the extrusion line with regard to certain frame conditions the cooling behavior of the heat storage modules have to be known. Therefore, it is necessary to determine the exact product properties, which are depending on material properties and the final shape of the module. Taking the temperature-dependent specific volume of the phase change material into account the shape of module’s shell is aimed to be the form of an elliptical prism. Considering the operating conditions of the heat and power plant and specific material properties a static mechanical analysis and an exact determination of material properties are made to design the final dimensions of the module’s shell.