A method for manufacturing a structure reinforced by fibers, the method comprises: (i) providing a mandrel of a first material, wherein the mandrel comprises an outside surface, a hollow interior, and an aperture for allowing a fluid to enter the interior, the first material is rigid at room temperature and has a melting temperature at which it melts, and the first material becomes deformable when approaching the melting temperature, (ii) providing a layer of a second material on the outside surface of the mandrel without blocking the aperture by applying one or more sheets of the second material on the mandrel, wherein the one or more sheets have an adhesive side allowing the one or more sheets to adhere to the mandrel and/or to each other, wherein the second material comprises an uncured thermo-setting resin and fibers configured for reinforcing the structure, the second material has a curing temperature below which it is pliable and above which it cures, (iii) placing the mandrel and the layer in a mold cavity formed by a mold, wherein the mold is configured to allow a fluid to reach the aperture of the mandrel, (iv) introducing a pressurized fluid into the interior of the mandrel via the aperture for generating a force acting to expand the mandrel outward, heating the mandrel to a temperature below the melting temperature of the first material for making the mandrel deformable and allowing the mandrel to expand outward and press the layer against the mold, and heating the layer to a temperature above the curing temperature of the second material to cure and form the structure, (v) heating the mandrel to a temperature above the melting point of the first material for melting the mandrel, and (vi) removing the melted mandrel from the structure. (i) providing a mandrel of a first material, wherein the mandrel comprises an outside surface, a hollow interior, and an aperture for allowing a fluid to enter the interior, the first material is rigid at room temperature and has a melting temperature at which it melts, and the first material becomes deformable when approaching the melting temperature, (ii) providing a layer of a second material on the outside surface of the mandrel without blocking the aperture by applying one or more sheets of the second material on the mandrel, wherein the one or more sheets have an adhesive side allowing the one or more sheets to adhere to the mandrel and/or to each other, wherein the second material comprises an uncured thermo-setting resin and fibers configured for reinforcing the structure, the second material has a curing temperature below which it is pliable and above which it cures, (iii) placing the mandrel and the layer in a mold cavity formed by a mold, wherein the mold is configured to allow a fluid to reach the aperture of the mandrel, (iv) introducing a pressurized fluid into the interior of the mandrel via the aperture for generating a force acting to expand the mandrel outward, heating the mandrel to a temperature below the melting temperature of the first material for making the mandrel deformable and allowing the mandrel to expand outward and press the layer against the mold, and heating the layer to a temperature above the curing temperature of the second material to cure and form the structure, (v) heating the mandrel to a temperature above the melting point of the first material for melting the mandrel, and (vi) removing the melted mandrel from the structure.