An empirical and a theoretical analysis is developed and employed to predict the stiffness of doubly curved surfaces such as those found in exterior automotive body panels. The dependent variable stiffness is a function of the independent panel variables which are: 1. Panel principal radii of curvature. 2. Panel chord lengths. 3. Panel thickness. 4. Panel boundary conditions. The empirical analysis based on measurements made on actual automotive panels substantiates the theoretical analysis based on finite-element computer techniques. Finally, the finite-element technique is used to compute the curvatures required for an aluminum panel to maintain the same stiffness as a steel panel.