Abstract: A method of manufacturing wire from a conductor and a supply of thermoplastic insulating material. The method involves heating the insulating material, adding pressurized gas to the material, and extruding a sheath of the insulating material about the conductor to generate bubbles of the gas in the sheath. The method may operate by limiting the temperature of the material prior to extrusion, to increase viscosity to limit bubble expansion, and may provide a significant pressure drop on extrusion by limiting the gap between a wire-supplying guide and the extrusion die.