NGK standard plugs are constructed for longer life and optimum performance. Nickel is a hard, inexpensive metal used in most all spark plug designs. Nickel is not a good conductor and has a high level of resistance, so most center electrodes feature a copper core, covered in a nickel-alloy. This creates a balanced, team effort where the copper core conducts electricity and promotes heat dissipation, and the nickel-alloy outer material prolongs the life and durability of the center electrode. While nickel is a choice material used in the majority of spark plug designs, it has its limitations. Other materials are harder, stronger, have a lower electrical resistance and a higher melting point, and are therefore used to enhance nickel electrodes and prolong a plugs life in high performance designs.