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Since the monolithic ceramic substrate was introduced for automotive catalytic converters, the reduction of the substrate wall thickness has been a continuing requirement to reduce pressure drop and improve catalytic performance. The thin wall substrate of 0.10 mm (4 mil) thick wall/400 cpsi cell density has been introduced to production by achieving mechanical strength equivalent to a conventional 0.15 mm (6 mil)/400 cpsi substrate. Although a round cross-section substrate can have a reduced catalyst volume compared to an oval cross-section substrate because of uniform gas flow distribution, the smaller cross-section of the round substrate increases pressure drop. The thin wall technology was applied to the round substrate to offset the pressure drop increase and to further improve catalytic performance.

A new alumina mat for a ceramic catalytic converter was developed which is capable of reliably holding a ceramic catalyst carrier up to 900°C. This alumina mat is composed of a fibrous material consisting of 80% by weight of Al2O3 and 20% by weight of SiO2, provides a high surface pressure. The mat has a packing density of 0.2-0.4g/cm3, and can provide not only reliable catalyst holding but also weather resistibility and exhaust gas interception. The mat also has a structural reliability based on the ceramic fatigue theory.