Copper welding is not hard. The heat required for this type of welding is approximately twice that required for steel of similar thickness. Copper has a high thermal conductivity. To offset this heat loss, a tip one or two sizes larger than that required for steel is recommended. When welding large sections of heavy thicknesses, supplementary heating is advisable. This process produces a weld that is less porous. Copper may be welded with a slightly oxidizing flame because the molten metal is protected by the oxide which is formed by the flame. If a flux is used to protect the molten metal, the flame should be neutral. Oxygen-free copper (deoxidized copper rod) should be used rather than oxygen-bearing copper for gas welded assemblies. The rod should be of the same composition as the base metal.