The thermal management of battery systems is becoming increasingly important with the gaining demand of electric vehicles. Nonetheless, no convincing solutions for thermal insulation foils are able to avoid thermally initiated chain reactions between adjacent battery modules in the event of thermal runaway. Therefore, the aim is to develop an innovative thermal insulation membrane. The main idea is to design a material exhibiting decreasing thermal conductivity properties with increasing temperatures. This material behaviour is caused by expandable flake graphite, a form of intercalated graphite. Due to the expansion process, the free volume increases resulting in a reduced thermal conductivity of the material. The expansion of the utilized flake graphite is starting at temperatures around 150°C. The flakes and further additives are embedded into a dual-component silicone resin. During the product development, a number of different material tests are performed in order to characterize the material behaviour at different conditions. Evaluation of the thermal stability of the insulating foil is of paramount importance in the design process. Furthermore, uniaxial tensile and compression as well as biaxial tensile tests are conducted with different mid-layer configurations of the insulation composite to analyse the influence of different fillers. Additionally, the test data is made use of to determine the parameters of known hyperelastic material models for the matrix material. Uniaxial compression tests in addition to the standard uniaxial tensile tests are performed as the insulating layers primarily absorb compressive loads.