To reduce greenhouse gas emissions, electrification is the biggest trend in the current-day automotive industry. In this transition, important topics are efficiency and weight reduction. This study focuses on the application of composite materials for the undershield of an automotive rechargeable energy storage system (REESS). In this application, the undershield forms the structural floor of a battery enclosure. The goal of the research was to determine if the homologation and safety demands for the undershield can be met with a composite-dominant design. Additionally, the goal was to determine if such a design can result in mass, cost, and emissions improvements compared to current metallic designs. Based on European and Chinese homologation documents, SAE standards, and demands by Volvo Cars, a set of relevant requirements was constructed. Based on these requirements, a sandwich design proposal was done and potentially suitable materials were identified. Multiple material configurations for the design were then verified based on the driving requirements. Lastly, a performance comparison was done of the mass, cost, and CO¬2 emissions of each configuration. The results indicate that it is feasible to meet the homologations and safety demands for the undershield of an automotive REESS with a composite sandwich design. Using polyester or phenolic glass fiber SMC for the top face of the sandwich can provide a successful fire protection barrier. PET foam was identified as a low emissions core material for improved impact protection in combination with steel or PP GMT bottom plate. Additionally, lower costs and emissions can be offered with steel configurations compared to current metallic designs. Alternatively, PP GMT configurations offer mass and emissions reductions. All in all, the research has succeeded in demonstrating the potential of composite or hybrid designs for the application in an automotive REESS for the improvement of mass, cost, and/or greenhouse gas emissions.