The paper is devoted to the research results dealing with the development of heat-resistant composite cellularmaterial, where polymer matrix is based on10% polycarbosilanesolution in xylene, hollow microspheres and fibrous mineral material are used as fillers. In this study, the used hollow microspheres are corundum and aluminosilicate microspheres, and fibrous filler is quartz fiber. According to the experiments, the best results refer to thecomposite foam samples, containing hollow corundum microspheres as filler. The developed composite foam is characterized with low thermal conductivity and density, good physical and mechanical properties,when polymer binder content was 20-70% wt., corundum hollow microspheres - 20-60% wt., and quartz fiber material - 10-50% wt. Thus, the developed composite foam might be recommended for the applicationin high-tech industries, including heat and power engineering, nuclear power and aircraft construction as high-temperature thermal insulation material.