A filler metal is the material that is used in welding to join the two metal pieces together.  Its main purpose is to fill the gap between the two pieces or to add extra reinforcement metal. Filler metal melts, flows into the weld puddle, and freezes just as the base metal does to become a part of the completed weld. There are three different types of filler metals:

● Covered electrodes (used in stick welding)
● Bare electrode wire or rod (used in MIG & TIG welding)
● Welding fluxes (used in brazing)

Covered Electrodes are the most popular type of filler metal and are primarily used in shielded metal arc welding. They have a coating of a special composition material over them, which determines the electrode’s properties, the welded mold, and the usability of the electrode. Additives are added to the electrode to improve overall performance as well as weld performance. Common additives include: cellulose, metal carbonate, titanium dioxide, calcium fluoride, iron power, and sodium silicate (most popular).

Bare/Solid Electrode Wires are used in gas metal arc welding (MIG) as opposed to bare/solid electrode rods that are used in gas tungsten arc welding (TIG). Generally, the wires have a thin copper coating which enhances the current pickup.