Ford Racing Cat-Back Exhaust Systems are made of 409 stainless. This exhaust material is titanium stabilized ferritic stainless steel. 409 stainless is used in applications where appearance is a secondary consideration to mechanical properties and corrosion resistance and where some weldability is required. An example of 409 stainless usage is catalytic converter assemblies. 409 stainless has excellent forming characteristics and is rust-through resistant. A surface rust will form in most instances. This rust retards further corrosion.