While researching for this question, I came across a couple of conflicting images of Superman in space.
First we have him in space with no helmet - and talking to another character.
But then we have him in space with a helmet.
Now, you could easily argue that the helmet wouldn't really do much there as there is no oxygen tank, but the image still implies that he needs to breathe. The first image, however, really contradicts that though. I found other images of him speaking in space without a helmet, but I think the one image demonstrates the point well enough.
So, which is it?