Abstract: A method for producing a hollow part formed from at least two portions joined together along respective adjacent edges, or at least portions of such edges, producing at the same time a seal in the region of the assembly zone, the method consisting in producing a first portion by moulding of a first thermoplastic material, this first portion comprising at least one rib or ridge protruding in the region of its edge or its assembly edge portion, then in producing a second portion by moulding onto the first portion of a second thermoplastic material, with at least partial overmoulding of the edge or the assembly edge portion of the first portion by the second material mass forming the edge or the assembly edge portion of the second portion, or an extension of this edge, said second material entirely covering said at least one rib or ridge.