Insulating method of carbon filament and method for forming a coaxial cable with carbon filament and electric conductor

It is particularly an object of the present invention to provide a method for insulating a heater element and carbon filaments which prevent an insulating material from peeling off due to thermal expansion or air expansion, which exhibit the enhanced insulation performance and realize heat resistance and incombustibility, and which are electrically stable even in high temperature areas. This invention comprises: a collecting and twisting step of collecting and twisting thousands to hundreds of thousands of polyacrylonitrile carbon filaments, thereby, forming a collected and twisted body; a first coating step of coating the surface of the collected and twisted body with a synthetic polymer resin, thereby forming a single-layer coated body having a first coating layer; and a second coating step of coating the surface of the single-layer coated body with a synthetic polymer resin, thereby forming a double-layer coated body having a second coating layer over the first coating layer.