A method for manufacturing a fiber reinforced structure includes the following. A mandrel of a first material comprises a hollow interior and an aperture that allows a fluid to enter the interior. A layer of a second material provided on the mandrel includes an uncured resin and fibers. The mandrel and the layer are placed in a mold cavity formed by a mold. A pressurized fluid is introduced into the interior of the mandrel via the aperture to generate a force acting to expand the mandrel outward. The mandrel is heated so that it becomes deformable and expand outward to press the layer against the mold. The layer is heated so that it cures. The mandrel is then heated to a temperature above its melting point of the first material so that it melts, after which it is removed.