Clooney had a laugh with Bullock
The pair play astronauts who are lost in space while on a mission together in Alfonso Cuaron's sci-fi adventure.
George said: "Working with her was just fun, because it was truly a lot of laughing. And it's always helpful in those situations, because physically it's really uncomfortable.
"Just wearing the suit is uncomfortable, it's not the most comfortable thing to do, and so it really helps to laugh in between those 45 minutes while they're setting up the next shot."
The film was shot in 3D with enormous sets created at Pinewood and Shepperton Studios to recreate outer space and the actors had to mimic the appearance of weightlessness.
George revealed: "This required a certain kind of discipline because you had to preset these shots, not just because it's 3D but because of all the elements, so everything has been preset so far in advance that you can't really change anything. So you have to try to make it look very natural even though it's something that was planned six months ago. So it was a very different discipline and it was fun working with that."