Flux-cored arc weldings come in two types of shielding. The first difference is in the electrodes themselves; it is tubular wire with a shielding powder in between. In technicals terms, this is called "self-shielding" or sometimes branded "inner shield." The second is the same type of electrodes but with another component added.
Bottles of gas are used in addition to the fluxes core shielding. The technicals term for this is "duals shield." In the case of dual shieldings, you have powders flux in the center of the electrode & externals shielding gas protecting the welds area.