In order to meet and exceed ever-tightening automobile emission standards, more capabilities and performance are required from the complete engine exhaust system, including the catalyst substrate. Stringent emission standards demand that the emission control system be functional in the first 40 seconds after cold start. The UltraCat™ open-cell silicon carbide (SiC) foam catalyst substrate is designed for fast lightoff through incorporation of low mass and low heat capacity into a rugged, high temperature-resistant catalyst substrate with high heat and mass transfer characteristics. The unique combination of the open-cell foam structure and chemical vapor deposited (CVD) SiC allows the manufacture of an extremely corrosion- and temperature-resistant material, with 87% open frontal area, in a three-dimensionally interconnected open-cell structure that inhibits and minimizes the formation of boundary layers. The CVD SiC open-cell foam has undergone accelerated corrosion testing at temperatures up to 1300°C, and the UltraCat catalyst substrate has been incorporated into a close-coupled catalytic converter design and subjected to FTP testing. The results of both are presented. Also discussed are the strength, corrosion resistance, geometric surface area, and heat capacity of the SiC foam material, and the performance of the UltraCat catalyst substrate as a function of substrate volume, catalyst content, geometric surface area, and cell size.