Panel flutter is an aeroelastic phenomenon in which a thin plate subjected to supersonic flow exhibits unsteady bending oscillations. This problem has gained attention among researchers and in practice due to its importance in the design of high-speed aerospace structures. Since the seventies, work on optimizing these elements has focused primarily on achieving improved flutter performance while reducing structural weight. These studies have concentrated on the design of plates with variable thickness and composite plates. With the advancement of modern manufacturing methods, the design and fabrication of structures involving multiple materials and complex geometries have become feasible. In this work, we employ two different materials in the design of these panels to enhance flutter performance while reducing structural weight. We focus on a panel with an unknown material distribution in its plane, which defines the design space of the material optimization problem. The design variables determine the type of material at each point in the panel and are forced to converge to discrete solutions representing one of the two materials using the solid isotropic material parameterization (SIMP) approach. The optimization problem is solved using an efficient gradient-based framework with analytically derived sensitivities, developed in this study. A parametric investigation is presented to demonstrate the potential design improvements enabled by these bi-material configurations. Graphs showing the critical dynamic pressure as a function of structural weight for different material combinations are reported based on the optimal designs. The results show that the design of bi-material panels can maintain critical dynamic pressures comparable to those of standard homogeneous panels while achieving substantial weight reduction.