Can some tell me what is the other shell of an e-nail coil made of ? Apologies if that is already raised question in a thread,please point me to it. I see that some coils are black and others are shiny .. which is what ? The black ones might be stainless steel, it turns black after heater to red. After reading about coil heaters in general here is some general info. Insulation materials include ceramics, fiberglass, fluoropolymers, magnesium oxide, and mica. Ceramics consist of nonmetallic minerals, such as clay, that are permanently hardened by high-temperature firing. Most ceramics resist heat and chemicals. Fiberglass is strong, durable, and impervious to many caustics and extreme temperatures. Fluoropolymers, such as Teflon, are inert to most chemicals and extremely slippery. Magnesium oxide is a high temperature electrical insulator that is often in the form of a compacted powder. Mica is a colored or transparent mineral silicate that is crystallized in monoclinic forms and readily separated into very thin leaves. Mica is valued for its electrical insulating properties and resistance to heat and acids. Sleeve, sheath, or jacket materials include aluminum, brass, copper, fluoropolymer, iron, nickel alloy, rubber, steel, and stainless steel. So it seems it is some kind of steel but which one and why no ever mentions it,there are 1000s of places that cell it, and not even one lists the specifics of the sheath material. Is there any legit place to get coils with sheath out of Titanium or 316L ?