A process for manufacturing an electric cable including at least one core including a conductor and an insulating coating surrounding the conductor includes the steps of: providing a polyolefin material, a silane-based cross-linking system and a foaming system including at least one exothermic foaming agent in an amount of 0.1% to 0.5% by weight with respect to the total weight of the polyolefin material; forming a blend with the polyolefin material, the silane-based cross-linking system and the foaming system; and extruding the blend on the conductor to form the insulating coating. An electric cable includes at least one core consisting of a conductor and an insulating coating surrounding the conductor and in contact therewith, the insulating coating consisting of a layer of expanded, silane-cross-linked polyolefin material having an expansion degree of 3% to 40%.