Copper bonsai training wire is hand-coiled and kiln annealed* in the USA. The copper wire is solid, soft-drawn, and 99.9% pure. The copper wire is very malleable, with no hard spots, making for an easy application. As the copper wire is applied to your tree, it work hardens**, giving the wire greater holding strength over aluminum.
*Annealing is a heat treatment that alters the properties of the copper wire to increase its ductility and reduce its hardness, making it more workable. This involves kiln heating the copper to a suitable temperature and then quickly quenching it in water.
**Work harden is the strengthening of copper by deformation or applied force. In this case, transferred through the working of the wire.