Tungsten filament is a thin filament made by forging and drawing tungsten bars.

Tungsten filament is mainly used in electric light sources such as incandescent lamps and halogen tungsten lamps. Tungsten wire used as various luminous bodies in light bulbs also needs to be doped with a small amount of potassium, silicon and aluminum oxides during the smelting process. This kind of tungsten wire is called doped tungsten wire (Doped Tungsten Wire), also known as 218 tungsten wire or non-sag tungsten wire (Non-sag Tungsten Wire).

Tungsten wire is generally drawn by various wire drawing dies. The main purpose is to make filaments and high-speed cutting alloy steel. It is also used in optical instruments, chemical instruments and other aspects.

The resistivity of tungsten wire is 5.3*10^-8. Tungsten has a high melting point, high resistivity, good strength and low vapor pressure. It is the material for making incandescent filaments among all pure metals. However, tungsten is hard and brittle and difficult to process. When the current passes through the tungsten wire and is heated to a certain temperature, the resistance value of the tungsten wire increases to a certain value (the resistance value of the general metal wire increases with the increase of temperature). At room temperature, the resistance of this object should be 1370℃-2000℃, but when the cross-sectional area and length of the tungsten wire change, this resistance value will change. In 1909, Kulich invented the processing technology of tungsten filament, which played a decisive role in the production and promotion of incandescent bulbs. Its basic principle has been used to this day.