Automotive exhaust systems operate under service conditions that place severe demands on their materials of construction. Fortunately, there are several material choices available to the system design engineer. Among these materials are aluminum coated carbon steel, various grades of stainless steel and aluminum coated stainless steel. Each of these materials has its own unique set of properties, and they of course sell at different prices. The challenge to the design engineer is to develop a combination of material selections and system design that will meet his company's durability goals at the lowest possible total raw material and manufacturing cost. The North American market has widely adopted 12% chromium stainless steels for exhaust system applications. The forward or hot sections of the exhaust system are usually made from uncoated material, while a significant portion of the cold section material is coated with aluminum. There is also significant use of 18% chromium stainless steel, and minor use of austenitic stainless steel and aluminum coated carbon steel. The effects of design features on cold end durability are just beginning to be well understood. Optimized design offers the potential to maximize system life for any material of construction.