Abstract: The invention relates to a method for producing of a form part, especially of a plane thin-walled fiber composite part, in a mould (1), comprising the steps: a) Providing of the mould (1), wherein the mould (1) comprises a cavity (2) with a nominal form volume (V) for inserting of a reactive mixture, wherein the cavity (2) is delimited by at least one cavity wall section (3) which is elastically deformable during the inserting of the reactive mixture and wherein the modulus of compressibility (K) of the cavity (2) is between 2,000 bar and 10,000 bar; b) Inserting of the reactive mixture into the cavity (2), wherein the reactive mixture is inserted with such a pressure into the cavity (2) so that the cavity volume is increased during the insertion of the reactive mixture due to elastic deformation of the at least one cavity wall section (3) above the nominal form volume (V); c) Letting solidify of the reactive mixture in the cavity (2); d) Demoulding of the finished form part from the mould (1).