In one aspect, there is disclosed a high temperature composite insulation assembly for a fuel cell that includes a core portion having inner and outer surfaces. A temperature stable sealant is disposed on the outer surface of the core portion forming a gas retaining mechanically robust insulation assembly. In another aspect, there is disclosed a high temperature composite insulation assembly for a fuel cell that includes a core portion having inner and outer surfaces, and a reinforcing material disposed on the outer surface of the core portion. A temperature stable sealant is disposed on the outer surface of the core portion forming a gas retaining mechanically robust insulation assembly. In another aspect, there is disclosed a high temperature composite insulation assembly for a fuel cell that includes a core portion having inner and outer surfaces and a high temperature refractory material disposed on the inner surface of the core portion. A reinforcing material is disposed on the outer surface of the core portion and a temperature stable sealant is disposed on the outer surface of a core portion forming a gas retaining mechanically robust insulation assembly.