Abstract: The process makes use of a lost core of polystyrene, on which are wrapped and compacted, in successive stages, various sheets or mats of carbon fibre, of known type; a first compaction is effected in an autoclave after having sealingly wrapped the core, before lamination of the carbon fibre layers, in a first polythene envelope, and after having sealingly wrapped the partly finished product constituted by the core wrapped in the first polythene envelope and some of the carbon fibre sheet or mat in a second polythene envelope, by creation of a vacuum within the interior of the second envelope, while maintaining the interior of the first envelope in communication with the outside of the second envelope; a second compaction, after removal of the second envelope, following lamination of further sheets or mats and possible mounting of metal inserts on the core and insertion of the partly finished product thus obtained between a pair of mould halves, is effected in an autoclave by wrapping the two mould halves, pre