An EPP interior (or a complete case) can be really interesting for some applications. EPP (or Expanded PolyPropylene) is really shock absorbent and highly insulating. This material is also resistant to acid, oils etc., which makes it very useful for storing and transporting tools and machines. EPP parts are available in every colour.
For making an EPP-interior you need a mold. Therefor every shape can be made. The downside is that you have to invest in the mold, so it is mainly interesting for higher quantities.