Iridium is a precious, silver-white metal and one of the densest materials found on earth. The natural properties of Iridium offered NGK the opportunity to create one of the world's finest spark plugs. The result are spark plugs that require less voltage to spark, burns fuel more efficiently, sparks at leaner air/fuel mixtures, and delivers higher horsepower and better gas mileage. NGK offers the new Iridium IX® - The ultimate evolution of a performance spark plug.