This paper introduces a new mechanism for achieving tunable stiffness, named layer jamming, and presents a hollow snake-like manipulator having tunable stiffness capability. The layer jamming mechanism is composed of multiple layers of thin Mylar film, and makes use of amplified friction between the films by applying vacuum pressure. In contrast to other tunable stiffness technology, such as particle jamming or field-activated materials (MR or ER fluids), layer jamming occupies a small volume and thus can be applied to small, light weight manipulators. The snake-like manipulator presented here is composed only of Mylar film and wires, and has highly flexible and under-actuated properties without application of a vacuum; however, it becomes highly stiff when a vacuum is applied. In this paper the characteristics of layer jamming are explored: its stiffness and breaking strength are obtained both theoretically and experimentally, and a prototype manipulator is developed and experimentally characterized.