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. The improved flow properties of a metal substrate mean that, for a given level of pressure drop, a metal substrate can be made with a greater cell density than the ceramic alternative.

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