In an insulating system for high-voltage machines, a three-layer insulating tape is proposed as turn-to-turn insulation which comprises a center mica layer (1) which is covered on both sides by plastic foils (2,3) having different thickness. Thermoplastic adhesive layers (4,5) on the outer surfaces of the foils (2,3) produce an intimate bonding of the turn-to-turn insulation to the conductor elements and to the main insulation. An insulation of such construction is distinguished by a high electrical life at increased temperature and a high surge withstand capability.