Slag

• Flux cored welding will produce slag, which is a protective coating over the weld that needs to be removed before painting. MIG does not, as it uses gas.
  
  

Wire

• MIG wire is solid metal, and flux core wire is comprised of steel on the outside, and the flux on the inside, hence the name.
  
  

Nozzle

• MIG welding guns have a cylindrical nozzle on the end that routes the gas onto the new weld. Because flux core welding does not use gas, no nozzle is necessary.
  
  

Material

• Flux cored welding will penetrate deeper into the metal than MIG welding at the same amperage. Therefore, flux core is not very good on thin metals, whereas MIG works well.
  
  

Location

• Because MIG welding uses protective gases that can blow away from the weld if there is a breeze, flux cored welding is recommended for outdoor use.
  
  

Polarity

• Flux core wire requires a DC negative (DCEN) setting on the welder in order to work properly, and MIG welding is a DC positive (DCEP) process.