Tightening global emissions standards are driving automotive OEM’s to utilize TWC aftertreatment systems which can perform with greater efficiency and show a greater measured control of PGM (Precious Group Metals) usage while at the same time minimizing exhaust system pressure drops. This study is targeted to quantify the influence of catalyst substrate cell geometry on emissions and PGM usage. Additionally a study of light-off and back pressure comparisons will be made. The two substrate configurations used are Hex/750cpsi and Square/750cpsi. It will be shown that the Hex design can (1) reduce emissions and/or PGM by high active GSA (Geometric Surface Area) with faster light off, and (2) reduce back pressure by increased OFA (Open Frontal Area) of the hex geometry.