A resin impregnated paper (RIP) condenser core configured for being positioned around an electrical conductor. The condenser core includes a winding tube forming a longitudinal through hole through the condenser core, configured for allowing an electrical conductor to be inserted there through; an electrically insulating RIP body wound onto and around the winding tube; and at least one electrically conducting foil coaxially encircling the winding tube and being surrounded by the RIP body insulating each of the at least one foil from any other of the at least one foil. The winding tube is of an electrically insulating material which has been chosen from a group consisting of materials having a volumetric thermal expansion coefficient within the range of 50% to 200% of the volumetric thermal expansion coefficient of the RIP body.