I would always think it was some sort of matter rather than a hard surface. I feel like they would have the technology to change it.I am thinking it would have to be lightweight & non-magnetic. Something that would help propulsion.
Something like that. Probably something that we would make up but they're so advanced in tech that they can do it.You mean like, liquid metal or something, with the shape held together with magnetism? (just made that up).