HIPS is high impact polystyrene - a type of plastic. It's thin compared to ABS, which most suits are made of, but since you shouldn't be bumping your helmet around on things, it's fine for buckets. The thinner plastic also shows more detail than a thicker plastic. You want to avoid this seller because he is recasting AP parts. AP is a seller here and you should support him instead of supporting the guy ripping him off.