Tungsten wire's resistivity is 5.3*10^-8, tungsten melting point, high resistivity, good strength, low vapor pressure, is all pure metal to make the best tungsten filament incandescent material. But tungsten is hard and brittle, making it difficult to process. When an electric current is heated through a tungsten wire to a certain temperature, the resistance of the tungsten wire increases to a certain value.

At room temperature, the resistance should be between 1370℃ and 2000℃. However, when the length of cross-section of tungsten wire is changed, the resistance value will change. In 1909, Coolidge invented the processing technology of tungsten wire, which played a decisive role in the production and promotion of incandescent bulb, and its basic principles have been used to this day.