Flexible 304 stainless steel with yellow polyethylene jacketing. All tubing clearly marked with gas pressure rating, EHD (Equivalent Hydraulic Diameter). Tested to the ANSI Standards for Fuel Gas Piping System using Corrugated Stainless Steel Tubing(CSST), ANSI LC-1a-2009, CSA 6.26a-2009, ANSI LC-1-2005 and CSA 6.26-2005.Cost-saving alternative when electrical bonding is requiredCost-saving alternative when electrical bonding is requiredExtraordinary labor savings compared to black steelAnnealed no spring back, tube bends and stays bent