Portable and motive applications of open-cathode polymer electrolyte fuel cells (PEFCs) require not only good stack performance but also a light and compact design. In this context, we explore how edge cooling with three different fin designs—one standard rectangular fin and two triangular fins that essentially halve the size of the fins—can improve the thermal and water envelopes inside the stack as well as stack performance while reducing the overall volume. The results suggest that all three edge-cooling designs give rise to lower and more uniform local temperature distributions as well as higher and more uniform hydration levels at the membrane in the stack compared to the conventional open-cathode PEFC without fins and design with additional air coolant plates. In addition, edge cooling design with one of the triangular fins yields the best performance (around 5% higher in term of power per unit catalyst area and power per unit weight as well as ∼10% higher in term of power per unit volume as compared to other designs). Overall, the triangular fin design shows potential to be used in, for example, automotive applications due to its high performance as well as lightweight and compact design.