Silicone elastomers are high-performance plastics. In the extrusion process, only high-consistency silicone rubbers were used. In order to reduce the cost and weight, silicone rubbers can be foamed during processing. In this study, high-consistency silicone rubber is processed with different physical and chemical blowing agents. The resulting reaction kinetics, as well as the mechanical and morphological properties, had been investigated and compared with each other. This showed that the chemical blowing agent significantly influenced the crosslinking reaction compared to the microspheres and the water/silica mixture tested, but it also achieved the lowest density compared to the physical blowing agents. When evaluating the foam morphology, it became clear that the largest number of pores was achieved with the microspheres and the largest pores when using the water/silica mixture. Furthermore, it has been shown that the different mechanisms of action of the blowing agents have a major influence on the mechanical properties, such as the micro shore hardness and the foam morphology.