An extrusion method and apparatus (11) for producing a cable (1, 101) including at least one core (7) comprising at least one transmissive element (2, 40), and at least one pair of coating layers (8, 9) arranged at a radially outer position with the respect of the core (7) are described. The method of the invention includes the simultaneous steps of depositing by co-extrusion at least one coating layer (8) of polymeric material and one coating layer (9) of expanded polymeric material and of maintaining a residual pressure not greater than the external pressure in a substantially annular interspace (21) defined between the coating layers. With respect to the methods of the prior art, the present invention allows to avoid the formation of bubbles at the interface between said at least one coating layer (8) of polymeric material and the coating layer (9) of expanded polymeric material, attaining an optimal adhesion between said layers (8, 9).