A composite part comprises a sheet of fiber-reinforced thermoplastic material and a sheet of non-reinforced thermoplastic material superposedly attached together. Both sheets are iointly deformed substantially differently along different axes. A tool for manufacturing the part made of the sheet of thermoplastic material comprises a female die and a male die. The female die has a cavity, whose wall has a bottom portion and a top portion. The male die has a backing structure, a support attached to the backing structure and a heat-resistant bladder. A method of manufacturing the part made of the sheet of thermoplastic material comprises the step of applying pressure on the thermoplastic sheet against the wall of the female die from the bottom of the female die to a splitting line of the female die by inflating a deformable portion of the male die.