A conductor for windings cooled by liquid, especially for transformer windings, has an insulating covering which surrounds the entire conductor (1). At least one layer (2) of the covering completely surrounds the conductor (1). An external layer (3) provided with at least two layers (2, 3) of the covering comprises openings (4), holes (5) or frays (6) through which a coolant flowing around the conductor is placed in a turbulent state and better heat exchange is obtained.