Modern magnet wire typically uses one to four build thicknesses (in the case of quad-film type wire) of polymer film insulation, often of two different compositions, to provide a tough, continuous insulating layer. Magnet wire insulating films use (in order of accelerating temperature range) polyvinyl formal (Formvar), polyurethane, polyamide, polyester, polyester-polyimide, polyamide-polyimide (or amide-imide), and polyimide. Polyimide insulated magnet wire is capable of continuous operation at up to 240 °C. The insulation of thicker square or rectangular magnet wire is often augmented by wrapping it with a high-temperature polyimide or fibreglass tape, and completed windings are often vacuum impregnated with an insulating varnish to enhance insulation strength and long-term reliability of the winding. Self-supporting coils are wound with wire coated with a minimum of two layers, the outermost being a thermoplastic that bonds the turns together when heated. Other types of insulation such as fibreglass yarn with varnish, aramid paper, kraft paper, mica, and polyester film are also widely used across the world for various applications like transformers and reactors. In the audio sector, a wire of silver construction, and various other insulators, like cotton (sometimes permeated with some quite coagulating agent/thickener, like beeswax) and polytetrafluoroethylene (Teflon) can be found. Older insulation materials included cotton, paper, or silk, but these are only useful for low-temperature applications (up to 105°C). For simple manufacturing, some low-temperature-grade magnet wire has insulation which will be removed by the warmth of soldering. This means that electrical connections at the ends are often made without stripping off the insulation first.