They're called gummi ships, but they're not made of candy. It's...

[Okay, he has to back up a little. What's up with his world that he always has to explain things?]

The universe I came from is lots of small worlds, rather than one big one like this. Until maybe ten or twelve years ago, there were physical walls in the way. When those walls started to crumble and the pieces fell onto the worlds, people used them to build ships. Because they're made of the barriers, they can protect the passengers from the effect of the space between the worlds.