A flux core wire is optimized to obtain performance which is not possible with a solid wire. For many applications like vertical-up welding, flat welding, welding over galvanized, or welding hard to weld steels, a flux core wire can do it better and faster. Gas metal arc welding with a solid mild steel wire is popular easy to use and effective for many applications. There are two types of flux-cored wire electrodes: gas shielded and self-shielded. The flux coating on gas-shielded flux-cored wires solidifies faster than the molten weld material.  Consequently, a sort of shelf is created which holds the molten pool when welding overhead or vertically up.