The paper seeks to establish rational criteria for evaluating the structural efficiencies of sheet-stiffener combinations and alternative constructions used for wing and other surfaces, and to determine the suitability of the available materials for panels of various proportions. The efficiency criteria require the determination of the ideal construction for such panels, and this is carried out. It is found that the primary requirement of the “best” material for the ideal design is a high strength-weight ratio (yield stress-density). A diagram (Fig. 5) is given to determine readily the weights of panels of ideal design made of various materials, all to carry the same load. In general one material is better than another only for a limited range of panel proportions.