8/ A mold for injection molding an optical article out of thermoplastic material, the mold comprising two half-blocks each possessing at least one mold recess defined transversely by the working face of a shell provided with heat-transfer means that are intrinsic and both-way, said shell including a base receiving all of the heat-transfer means of said shell and a removable insert fitted on the base and carrying the working face, said insert having no intrinsic heat-transfer means and being thermally regulated solely by heat transfer with said base, the insert being cap-shaped and fitting over a head portion of at least the base, and the heat-transfer means of the base being allocated to the head portion of the base that is covered by the insert, the blocks being movable relative to each other between an open configuration and a closed configuration in which the two half-blocks make contact via junction faces in a transverse join plane and in which the recesses co-operate in pairs to form the desired mold cavity(ies).