Abstract: A barrier is formed on a metal substrate by coating the substrate with a metal oxide, calcining the substrate, impregnating the coated substrate with an acid, and calcining the impregnated coating at a temperature high enough to cause the metal oxide to form the barrier. The resulting barrier acts as an excellent electrical insulator, and also provides improved resistance to abrasion, and improved adhesion to the substrate. The particles forming the barrier also have improved cohesion. The metal substrate having the barrier of the present invention can be used in electrically heated catalytic converters, where it is necessary to provide closely spaced layers of metal foil that must be electrically insulated from each other. The invention can also be used in other metal structures intended to be placed in the exhaust stream of a chemical or manufacturing process or an engine.