A strategy to design stable ion-conducting membranes is presented. The basic idea is to sandwich a core layer of a suitably selected material between two thin side layers of a different material. The function of the side layers is merely to stabilize the core layer. This strategy is very versatile because a large variety of otherwise unusable materials can actually be stabilized into a core layer and utilized as an electrolyte membrane. To demonstrate these concepts poly(vinyl alcohol)-poly(styrene sulfonic acid) (PVA-PSSA) blends sandwiched between two thin Nafion layers were prepared by hot-pressing the three layers or by airbrushing a Nafion solution onto both sides of a PVA-PSSA layer. The composite triple-layer membranes were investigated with regard to stability, ion conductivity, methanol permeability, and performance in H-2-polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells. Although the presence of ion-transfer resistance at the interfaces between the layers was observed in this special case, our results indicate, more generally, the "triple-layer membrane" concept as a viable generic approach to make stable, insoluble, ion-conducting membranes. Because the method can be utilized to prepare membranes with a wealth of materials, the membrane characteristics can be more easily engineered.