Lets talk about the science of superheroes. I know its fiction, and that anything can happen. But sometimes you can attempt to apply logic and science to them, and sometimes the comics do it themselves. I think it might be fun to try to explain things from the comics, like how is Superman bullet/bomb proof yet able to shake hands and be bumped into without people getting hurt from his steel skin? Or How does Spider-Man's Spider-Sense work? Recently Marvel explained how Sandman is really just one grain of sand that controls the whole body of sand, how about that? I also like how the Batman cartoon explained that Killer Croc is a normal human, sort of, with normal skin cells formed like crocodile scales all over his body. I'll start, Theories about how Superman's skin is invulnerable while still seeming human: Perhaps Superman maybe he has regular skin cells but they are denser and made differently because he is alien. So each cell is still a cell, but compared to our human cells they are denser and stronger and steel like, but because each cell is individual and because he has millions of them, he has a lot of give to his cells. So that his skin still feels like skin and can fold and bend, but its much denser as to not break or be effected by hard blows from an enemies punches or bullets. So, in the image here, imagine that each skin cell is hard as steel because they are made differently than ours. So his skin isn't a solid mass of steel. I also like the theory that his skin is similar to that substance that is soft when standing still but because hard when there is force. That stuff you can run across but if you stand on it you sink. Similar, but not exact, because he is an alien. But maybe, another theory, is that each cell is like that substance and can become hard when needed. Like a reflex. Like Spider-Man's Spider-Sense. Maybe when his skin needs to each cell becomes more solid. But when he doesn't need it they are soft like normal humans.