High silica glass fiber (hSGF) reinforced phenolic(PF)and phenolic foam (PFa) composites were prepared, and the structure and properties of the composites were characterized by Infrared spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results show that the hSGF/PFa composites have similar chemical structure and curing reaction temperature in comparison to hSGF/phenolic resin (PF) composites, and both have good heat resistance. The properties of the composites were investigated. The density and the thermal conductivity decrease from 1.65 g/cm³ and 0.5 W/(m·K) to 0.5 g/cm³ and 0.09 W/(m·K), respectively, with decrease of the mechanical strength, when the matrix was changed from PF to PFa.