Down-gauging outer panels is an effective method for reducing the weight of an automobile body. We have succeeded in narrowing the thickness of outer panels by using rib-shaped plastic reinforcement. The plastic reinforcement consists of unhardened resin and an adhesive sheet, and it conforms well to the curved panel surface. In the body paint oven, it is hardened on the outer panels and forms a rib-shaped structure.This paper describes the composition of the resin material, the manufacturing process and the strength and rigidity of outer panels made with the rib-shaped reinforcement. It also discusses the weight reduction effect achieved by applying these panels to the doors of a production vehicle.