Abstract: A complex-shaped, three-dimensional fiber reinforced composite structure may be formed by using counteracting pressures applied to a structural lay-up of wetted fibers. The wetted fibers are arranged on pressurizable members and may be configured to include internal structural features, such as shear webs. A reinforcement stiffener may be located adjacent to at least one of the pressurizable members and the wetted fibers that form the internal structural feature. The reinforcement stiffener includes a modulus of elasticity that is substantially higher than a modulus of elasticity of the resin used to wet the fibers. In one embodiment, the reinforcement stiffener may be received in a pocket of one of the pressurizable members and may include a releasing agent that permits removal of the stiffener after the composite structure has been pressurized and cured.