What is the best way to pad an instrument case to prevent damage?

In building a musical instrument case I want 2 inches of foam between the instrument and the wooden sides in all directions. Should I use the same soft foam all the way around, or have soft foam next to the instrument with about 2 different less soft foams to decelerate the contents in the event of a fall. I know this sounds like a school project but this is a "real world" question.