A DC-cable having at least one conductor and an inpregnated insulation system is disclosed. The insulation system comprises a solid electrically insulating dielectric part with a porous, fibrous and/or laminated structure impregnated with an oil that comprises a gelling additive. The gelling additive molecule, which molecule comprises a polar part, group or segment, interacts with the oil and/or any other gelling additive molecule to form a gelled network of longer and/or more branched polymer molecules or cross-linking bridges in the oil, which thereby exhibits the flow properties of a highly viscous and elastic gel.