The invention concerns an injecting method and a device for making bimaterial or multimaterial parts relatively at a relatively low cost and satisfying user requirements. The inventive device is characterized in that it comprises means for simultaneously or sequentially injecting into an impression (14) corresponding to a part (15) to be produced at least one first thermoplastic material to constitute an outer skin (16) of the part and at least one second thermoplastic material to constitute the core (17) of the part enclosed with said skin, said means including injection distinct nozzles (11a, 11b) arranged so as to correspond to distinct regions of the part and opening into at least one cold feeder channel (13) communicating with said impression (14).