Metal honeycomb substrates used in catalytic converters are made from extremely thin metal foil, typically with a thickness of just 0.05mm. By comparison the walls of a ceramic substrate may be four times thicker. For this reason, metal substrates offer less resistance to gas flow and therefore can accommodate a given flow rate with a lower pressure drop than an equivalent ceramic substrate.http://www.sheungwell.com/auto....-exhaust-purificatio