The design of interpenetrating polymer networks (IPNs) paves the way towards the preparation of materials with advanced properties, as they comprise the combined performance of different types of crosslinked polymers. The proper combination of polymer networks (e.g. duromers and elastomers) enables a tailoring of selected material properties without compromising on the processing behavior of the compounds. In this work, hydrogenated nitrile butadiene rubber (HNBR) was reinforced in situ with different thermosetting resin systems. Thermal crosslinking via independent reaction mechanisms yielded elastomer resin-based IPNs. The cured resin endows the HNBR with high reinforcement and substantially improves the material performance. The curing reactions of the resins and the IPNs were monitored via FTIR spectroscopy and MDR analysis, respectively, and AFM images were taken to assess the morphology and phase distribution in the cured composites. Mechanical testing along with equilibrium swelling experiments to determine the crosslink density were performed in dependence on the curing time of the produced IPNs. A structure-property relationship was established by correlating mechanical properties with the network structure and morphology. In situ reinforced HNBR composites with excellent thermo-mechanical properties were developed by optimizing the compound composition, and the material behavior was found to be stable against variations in the processing method.