Abstract: A stack formed by layers of bidimensional fabrics or layers of parallel threads extending alternately from one layer to the next in a first direction and a second direction is sewn in parallel lines by means of a thread which extends in a third direction. The layers are stacked on a support of pyrolyzable material, the stack and the support being sewn by means of the thread which extends in the third direction. The assembly thus obtained is subjected to a temperature between 800.degree. C and 1200.degree. C in a stream of gaseous hydrocarbon in order to pyrolyze the material which constitutes the support and to deposit pyrolytic carbon on the threads which form the three-dimensional fabric.