Artists who model forms using soft, pliable materials, such as clay or wax, sometimes employ this kind of support when creating their work.

The correct answer is armature.

It is the skeleton of something - artists often use armature in order to support something else. So, beneath these soft, pliable materials, such as clay, or wax, you can find an armature made of metal usually, which is there to make sure the whole thing doesn't fall apart.