Abstract: Carbon-carbon composites consisting of graphite fibers reinforcing a carbon matrix are protected from oxidation by a B.sub.2 O.sub.3 glass coating which includes a refractory oxide to stabilize the viscosity of the glass. Precursors of B.sub.2 O.sub.3 and the refractory oxide are dispersed into a resin, the resin is used to impregnate fibrous graphite or fibrous graphitizable material, the sheets are laid up as plies and the laid-up plies are carbonized and graphitized using heat structure. The composite structure is then coated with an additional mix of resin and precursors and the coated structure is heated to carbonize the resin and leave a seal coat on the structure. Then an outer shell of a refractory material is deposited on the structure.