we have created different material groups to our material list, to help when creating components for different purpose. we have alum sheet metal, stainless sheet metal, steel sheet metal, and then structural. that's just what we have, giving an example.
then when you create a .par file, that is NON-sheet metal, so you choose the structural material group. when we create .psm it is for sheet metal parts, and you pick the correct type of material from the material groups.
just how we do it, sure others have different suggestions.