In recent years, materials with natural fillers have begun to be used for manufacturing window frames and various linings. These compounds can replace natural materials such as wood and stone. The main reasons to use these fillers are price (which is lower than that of a polymer) and rigidity. The resulting product is strong, hard, light, possesses a long-term resistance to wind abrasion and takes on the appearance of wood and stone. The type of filler has a significant effect on the final properties of the material. In the past, however, insufficient attention was paid to the effect of natural fillers on the injection-molded product's mechanical properties. First, the test samples were measured by depth sensing indentation (DSI), which is a contemporary instrumented hardness test used to determine the micro-mechanical properties. A Micro Combi Tester made by the Anton Paar company was used for these tests. Then, the measurements were evaluated by the Oliver and Pharr method. The goal of this study was to prepare a low-density polyethylene (LDPE) filled with varying natural fillers, e.g., finely ground wood, coarsely ground wood and slate) and its subsequent granulation. The implementation of these fillers led to an increase of the mechanical properties, e.g., indentation hardness and modulus, by up to 100 % in comparison with the virgin material. The goal of this study was to evaluate the effect of natural fillers, such as wood and slate, on the mechanical properties of the tested materials.European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Program [LO1303 (MSMT-7778/2014)]; Internal Grant Agency of TBU in Zlin [IGA/FT/2020/003
