Thermocouple wire represents a source of extotic alloys such as nickel-chrome, platinum-rhodium, and iron-constantan. Actually, most alloys used are refractory or noble metals and tend to be quite inert biologically. The insulation jackets are usually high temperature-tolerant polymers such as teflon. Thermocouple wires are often quite stiff and springy and may be very difficult or impossible to solder effectively without special fluxes.