Many higher quality metal caskets utilize a sophisticated magnesium rust inhibitor process called "cathodic protection".  Semi precious metal caskets such as bronze and copper do not offer this technology as they are naturally rust and corrosion resistant. Stainless steel caskets have made their appearance a few years ago offering the protection of semi precious metals at a much lower cost. Metal caskets are commonly manufactured in 20, 18 and 16 gauge metals which indicates the thickness of the steel.  Interiors are tastefully coordinated in a variety of materials form crepe, velvet and satin allowing for a range of pricing to meet a wide variety of budgets.