The battery enclosure may account for up to 20-30% of the total weight of a battery electric vehicle. Efforts to reduce the weight of the battery enclosure, and hence the entire vehicle, mainly revolve around efficient design and appropriate material selection. In a previous work, parametric and topology optimization were carried out to reduce the weight of a given battery enclosure structure, with structural steel as the material used throughout. In practice, materials like aluminum and composites (e.g. carbon fiber composites) are more commonly used. In this work, material replacement will be explored for further weight reduction. Existing efforts in this direction consider materials based on different factors such as density, yield strength, cost, machinability, effects on environment, fire protection capability, etc. In this work, a systematic approach will be considered for selecting the optimal material which reduces weight as well as maintains structural integrity of the enclosure. As in other works, different factors, such as yield strength, density, cost, etc. will be considered for the optimal choice of material. Multi material design will also be explored, combining desirable properties of more than one material for different parts to make the structure more robust. Simulations will then be performed to ensure that the temperature of the cells remains within a feasible range. Modal analysis will also be performed to ensure that the resultant structure has its fundamental frequencies above those encountered while driving. Thus, the resulting material selection will be shown to ensure both structural robustness and thermal feasibility of the enclosure design.