I've seen people using the "lost PLA/ABS" method of getting a metal objects from 3d printed (or not) plastic ones.

But increasing the size of the object the metal version can , well, get pretty heavy and also kind of expensive.

So I'm wondering is there some technique that can be used to create *hollow* metal objects by only having a plastic version of it (or its mold, or whatever) in the beginning?

PS. Yes I know the possible side effects of molten metal.