Light-red, rather ductile, extendible semi-noble metal. In humid air, copper forms a firmly adhering layer of red copper(l)oxide. If CO2, SO2, chlorides or similar are present, a green patina develops over the course of time which, like the 2O layer, protects the material below from further corrosion. Pure copper is frequently used as material for lines in the electrical industry. Due to its chemical resistance and high thermal conductivity, it serves as a material for boilers, heating pipes, cooling coils, etc. Copper coatings are available by copper plating.