The proposed project aims to explain the changes that occur during the temperature-induced conversion of aromatic and aliphatic siloxane resins to silicon oxycarbide SiOC. The subject of the research will be mainly SiOC precursors located in the transition state between the organosilicon polymer and the inorganic material. Furthermore, the effect of the degree of pyrolysis on the adhesion between the organosilicon matrix and silicate (basalt and glass) fibers in composites from partially pyrolyzed SiOC precursors will be studied in order to improve the properties of the composites. The development of new materials will focus on the increased stability of hybrid composite systems at long-term temperature exposure while maintaining mechanical resistance. In order to achieve this goal, in addition to the above-described understanding of the ongoing processes, the improvement of the surface layer will also be used. An important partial goal will be to optimize the shrinkage of pyrolyzed SiOC precursors, namely by incorporating micro- or submicro-powder filler SiOC, and its related SiC and SiO2 before pyrolysis itself.