Abstract: A check valve provides a one-way fluid passage from without to within a fluid bladder formed by a pair of plastic sheets sealed together about their periphery. The check valve is formed by a pair of superimposed films of thermoplastic material, generally equal in length, thermally bonded together at predetermined areas to define the fluid passage throughout the length of the valve. The inlet end of the valve has a V-shape edge with the apex pointing in a direction opposite the one-way fluid flow. Each of the films, adjacent the V-shape edge of inlet end, is sealed to one of the outer sheets where the valve enters the bladder by a seal line of similar V-shape. Each of the films has a high-gloss, cohesive inner surface and a matted, non-cohesive outer surface.