Firstly, copper has an excellent electrical conductivity of around 58 million siemens per meter. This high conductivity allows the current to flow efficiently through the coil, which reduces energy loss in the form of heat. 

Secondly, copper is highly ductile, which means it can be drawn into thin wires without breaking. This property is critical in transformer design because the wire must be thin enough to provide a large number of turns without breaking. 

Lastly, copper is highly malleable, which means it can be easily formed into any shape, making it easy to manufacture the coils.