This results in a lower tensile strength and increased ductility. This gives rise to metals' typical characteristic phenomena of malleability and ductility. Strength and hardness increase with only slight impairment of ductility or impact resistance. Lead's high density, low melting point, ductility and relative inertness to oxidation make it useful. This is a result of gold's properties of malleability and ductility. Hydrated, biopolymers generally have enhanced ductility and toughness. It also has good ductility and thermal conductivity. Toughness requires a balance of strength and ductility. These castings tend to have poor ductility, toughness, and fatigue resistance. Steel plates with high hardness and high ductility are used. The ductility of steel varies depending on the alloying constituents. This observation explains the low hardness and high ductility of single crystals of copper. Metals are often reinforced with ceramics to increase strength at the cost of ductility. All treatments of steel trade ductility for increased strength and vice versa. Rebar can be supplied with various grades of ductility.