An extrusion method and apparatus for producing a cable including at least one core having at least one transmissive element and at least one pair of coating layers arranged at a radially outer position with respect to the core. At least one coating layer of polymeric material and one coating layer of expanded polymeric material are deposited by co-extrusion simultaneously and residual pressure not greater than the external pressure is maintained in a substantially annular interspace defined between the coating layers. The method avoids the formation of bubbles at the interface between the at least one coating layer of polymeric material and the coating layer of expanded polymeric material, attaining an optimal adhesion between the layers.