brand: terrafirma tHESE PRODUCTS ARE Made from 1.5mm 409 stainless steel these pipes will considerably outlast the life of the original system. 409 is easier to bend and weld and is not prone to cracking due to vibration like other grades of stainless steel. Material specification; Grade 409 is a ferritic stainless steel. Although regarded as a general purpose chromium stainless steel the primary application for Grade 409 is automotive exhaust systems. Its applications are where appearance is a secondary to bendability and corrosion resistance and where welding is required. 409 resists atmospheric and exhaust gas corrosion. A light surface rust will form in most atmospheres; this rust prevents further corrosion but makes the surface undesirable for decorative applications.