In considering the choice of consumable to use for a particular welding job, the composition of the consumables must be similar to that of the parent materials used, which will yield a weld that is homogenous. In some cases, like when welding brittle cast irons, a filler that has a different properties from the parent materials can be used. The joint created is called a weldment and the weld formed is known to be heterogeneous.

It has been approved that when welding materials that have different tensile strengths, the consumable chosen should match the material with the lower tensile strength while the preheat temperature used should match what is required for the material with the higher tensile strength.