A method of forming a composite article from a work piece at elevated temperatures and pressures. The method steps include disposing within a pressure chamber the work piece in contact with a mold, disposing a substantially incompressible medium in the chamber so that the medium is capable of transferring a substantially uniform predetermined pressure to the surface of the work piece, disposing within the substantially incompressible medium a fluid filled elastomeric vessel in fluid communication with a source of high pressure fluid so that the vessel is capable of causing a substantially uniform predetermined fluid pressure to the substantially incompressible medium, and causing the vessel to produce a pressure in the range of 400 to 20000 psi (2.8 to 138 MPa) to be applied to the substantially incompressible medium.