Abstract: The invention relates to a method of manufacturing an integral article comprising a fiber-reinforced composite material. An inner tool body (12) of a cellular plastic material is provided, onto which an airtight sheet (14) of a flexible material is applied so as to fully encompass and seal the tool body (12). A plurality of layers (16) of fiber-reinforced composite material are then applied onto the outer surface of the airtight sheet (14), and an airtight vacuum bag (18) is in turn applied onto the outer layer of the composite material (16). The vacuum bag (18) is evacuated and the layers (16) of composite material compressed. The composite material is heat treated so as to cure the same. The vacuum bag (18) is then removed from the thus formed article. To form a hollow integral tank, the formed article is provided with a hole (22), and a solvent is poured therein to dissolve the cellular plastic material.