A method for shaping a fibrous preform comprising: (a) providing a substantially flat fibrous preform, said fibrous preform comprising of an assembly of fibrous materials bonded to each other by a resin binder; (b) providing an upper flexible diaphragm and a lower flexible diaphragm, said diaphragms being formed of an elastomeric material and are impermeable to gas; (c) providing a housing with a mold positioned therein, said mold having a non-planar molding surface; (d) holding the fibrous preform between the upper and lower diaphragms in an air-tight manner by creating a sealed pocket between the diaphragms; (e) positioning the diaphragms with the preform there between over the housing so as to define a sealed chamber bounded by the lower diaphragm and the housing, and such that the lower diaphragm is positioned above the molding surface; (f) removing air from between the diaphragms to establish a vacuum pressure of less than 95·10 3 Pa (50 mbar) and less than the pressure in the housing; (g) heating the fibrous preform to a temperature above the softening point of the resin binder; (h) creating a vacuum inside the sealed chamber between the lower diaphragm and the housing by removing air at a rate of 100 Pa/15 min (1 mbar/15 mins) or faster until a vacuum pressure of 95·10 3 Pa (950 mbar) or below is reached, while heating is maintained, whereby the diaphragms with the preform there between are pulled toward the molding surface and eventually conform thereto, thereby forming a shaped preform; (i) reducing the vacuum pressure between the diaphragms to 1000 Pa (10 mbar) or below; (j) cooling the shaped preform to a temperature that is below the softening temperature of the resin binder; (k) relieving the vacuum from between the diaphragms; (l) removing the upper diaphragm from the cooled preform while maintaining vacuum inside the sealed chamber between the lower diaphragm and the housing; and (m) removing the cooled, shaped preform from the lower diaphragm. (a) providing a substantially flat fibrous preform, said fibrous preform comprising of an assembly of fibrous materials bonded to each other by a resin binder; (b) providing an upper flexible diaphragm and a lower flexible diaphragm, said diaphragms being formed of an elastomeric material and are impermeable to gas; (c) providing a housing with a mold positioned therein, said mold having a non-planar molding surface; (d) holding the fibrous preform between the upper and lower diaphragms in an air-tight manner by creating a sealed pocket between the diaphragms; (e) positioning the diaphragms with the preform there between over the housing so as to define a sealed chamber bounded by the lower diaphragm and the housing, and such that the lower diaphragm is positioned above the molding surface; (f) removing air from between the diaphragms to establish a vacuum pressure of less than 95·10 3 Pa (50 mbar) and less than the pressure in the housing; (g) heating the fibrous preform to a temperature above the softening point of the resin binder; (h) creating a vacuum inside the sealed chamber between the lower diaphragm and the housing by removing air at a rate of 100 Pa/15 min (1 mbar/15 mins) or faster until a vacuum pressure of 95·10 3 Pa (950 mbar) or below is reached, while heating is maintained, whereby the diaphragms with the preform there between are pulled toward the molding surface and eventually conform thereto, thereby forming a shaped preform; (i) reducing the vacuum pressure between the diaphragms to 1000 Pa (10 mbar) or below; (j) cooling the shaped preform to a temperature that is below the softening temperature of the resin binder; (k) relieving the vacuum from between the diaphragms; (l) removing the upper diaphragm from the cooled preform while maintaining vacuum inside the sealed chamber between the lower diaphragm and the housing; and (m) removing the cooled, shaped preform from the lower diaphragm.