The invention relates to a process for treating a lignocellulosic material, preferably wood, comprising the following steps: (1) soaking of the material with organic fluid in order to dissolve at least 40% and at most 85%, in weight %, of the lignin of the material; (2) washing with organic fluid so as to discharge the dissolved lignin; (3) filling with a filling compound; and (4) finishing, so as to obtain a composite formed of a three-dimensional network of transformed filling compound incorporated into a cellulose and lignin network. The invention also relates to a composite structure able to be obtained in this way, and to any part comprising at least one such structure.