The objective of the thesis was to determine optical, thermal, technological and mechanical properties of extruded sheets of polyethylene, polypropylene and their blends for applications in the automotive supplier industry. For the characterization of the optical properties scanning electron microscopy and polarisation microscopy was chosen. The thermal characterisation was performed by differential scanning calorimetry (DSC). For the technological estimation measurements of the density, for the mechanical properties tensile and bending tests were performed. By means of differential scanning calorimetry the increase of the crystallinity in dependence of the storage time was shown. In density measurements these results were confirmed. Furthermore, the rise of crystallinity was strongly dependent on the material. Sheets of polyethylene showed a higher increase of the degree of crystallisation in comparison to sheets of polypropylene with a low initial crystallinity. In addition, a significant influence of the polypropylene component to the polyethylene basis within the compound composition was detected. The determined mechanical properties of the tensile and bending tests showed a good correlation to the results of the DSC-analysis. Materials of low crystallinity exhibited the lowest values for the elastic modulus and strength, and vice versa. Additionally, assimilable results for the compounds of polyethylene and polypropylene were determined. Furthermore, additional effects were shown for a specific material pairing propably due to phase separation.