All aluminum, except for a magnesium cross brace under the firewall and steel door hinges, the new XJ's structure is stiffer by 60%, is virtually resistant to corrosion and provides a safer structure. In a UK government study, the XJ displayed the best "real world" safety of any car in its class. The 339 separate pieces are formed from three types of aluminum alloy supplied by Alcan. Forming the various elements of the body is by casting, stamping, extruding and hydroforming. Aluminum's advantages in production include better "memory" than steel during the stamping process and greater control of quality than steel, all at less expense.