mentioned a material selection is made for the central insulation layer 21 and the outer insulation layers 23 a and 23 b so that the central insulation material or the spacer insulator has a higher hardness than the outer insulation material in such a way that at the pressure exerted during the compression process by the electrical conductors essentially only the outer insulation material but not the central insulation material is displaced and the thickness of the central insulation layer is therefore maintained essentially unchanged this is explained further with reference to fig9 during the compression process exerted by means of extrusion punches 25 a 25 b elongation of the outer insulation 23 a 23 b occurs by wrapping of the corresponding round conductor 13 a to 17 b during shaping during this compression process which is indicated by white arrows the outer insulation material must be elongated the resistance to elongation of the outer insulation material indicated by round arrows 31 a and 31 b must be smaller than the mechanical resistance force of the spacer insulator 21 against its residual deformation indicated in fig9 with a straight double arrow 33 this is achieved in that insulation materials with lower resistance force to transverse elongation are processed for the outer insulation but materials with higher hardness are used for the spacer insulator 21 special aspects of the flat cable according to the invention with particularly good suitability for differential signal transmission in the range of very high frequencies lying in the ghz range are considered with reference to fig1 to 16 an insertion loss that has the most uniform possible curve as a function of.