Actually ceramic materials make the best protection against missiles like bullets or meteorites. So an advanced race of star travelers would not use metal-skinn

Actually ceramic materials make the best protection against missiles like bullets or meteorites. So an advanced race of star travelers would not use metal-skinned ships, they would coat their vessels with a thick layer of porous rock. All we can see is that outer protective skin. Inside the star travelers live generation after generation patiently waiting until they find a habitable planet to take over.