The stringent emissions regulations, notably for cold start, have led to design modifications in each of the converter components, notably the catalyst support. With the faster light–off requirement, the catalyst support must have a lower thermal mass so as to reach the 50% conversion temperature as quickly as possible. Simultaneously, for higher warmed–up efficiency, the catalyst support must offer higher geometric surface area. Similarly, for improved fuel economy and for preserving engine power, the catalyst support must exert lower back pressure. Indeed, these three performance requirements might be met by certain thin wall ceramic substrates, including 400/4.5 and 600/4.3, which have 22% lower thermal mass, 25% higher geometric surface area and 8% larger open frontal area than the standard 400/6.5 substrate. Testing by automakers and international laboratories on engine dynamometers has verified the above advantages of thin wall substrates.This paper will focus on calculated and measured strength and physical durability of thin wall substrates, both mechanical and thermal, in the coated and uncoated states. Such a durability is critical for meeting the 100,000 mile vehicle life requirement specified by automakers. Both the strength and calculated thermal shock capabilities of thin wall substrates, before and after coating, are compared with those of standard substrates. These data show that thin wall substrates with a compatible washcoat system should provide adequate strength and thermal shock resistance to meet the automakers' 100,000 mile vehicle life requirement.