Borla Header Kits utilize mandrel bent tubing and are built of aircraft-quality T-304 stainless steel inside and out, not mild steel, not aluminum, not coated aluminum, and not just wrapped with stainless on the outside for show. T-304 stainless steel has the highest chromium content, making it the most resistant to corrosion and therefore the most desirable material for a long-lasting exhaust system. Each kit is rigorously tested before production for optimum performance and to ensure an original equipment level of fit. Borla engineers and manufactures all of their exhaust products in the USA and is so confident in their products they back them up with a Million-Mile Warranty.