I want to make parts for which I need a mould that has inside narrow areas where it will be hardly possible to get a bag inside properly, let alone get the mesh and peelply out afterwards. In such cases it seems to be a possibility to make a core first that will stay in the finished part and that is a little smaller than the mould to allow for the carbon material around it. Of course a second mould is needed to make the core. However I wonder what material the core should be made of. It should be pretty light, it must be possible to kind of cast it and it shouldn't be overly expensive. The first idea of mine was to use ordinary pu installation foam but probably there's other or better possibilities. Of course it would be super cool if the core would expand a little under vacuum to press the material against the mould but I don't know if this is feasible at all.