COMPOSITE POLYMER ELECTROLYTE MEMBRANE, ELECTROLYTE MEMBRANE WITH CATALYST LAYER, MEMBRANE-ELECTRODE ASSEMBLY, AND SOLID POLYMER FUEL CELL

A composite polymer electrolyte membrane including a polymer electrolyte and a porous substrate, and having a dry tensile modulus of 100 N/cm or more per width and a wet tensile modulus of 35 N/cm or more per width. Enhancing the mechanical characteristics of the electrolyte membrane results in providing an electrolyte membrane that achieves good dry-wet cycle durability.