After completion of 5000 hours of salt spray exposure test, all four insulated steel panels were evaluated for presence of spot rusting, and corrosion attack to the metal substrate protected by insulation. A small area of insulation from each sample was removed to inspect the condition of the metal substrate. Visual examination revealed that the metal substrate under the insulation was virtually free from any spot rusting or corrosion damage due to salt spray exposure testing. Furthermore, it appears that the protection of the metal substrate under the insulation is independent of insulation thickness.