When you blow up a balloon yourself, it just hangs from the string. But party balloons from the store float straight up. Why? They have a lighter kind of air in them, a gas called helium. So those balloons can float about 20 miles up into the sky, almost to outer space. And they can lift things: In the craziest record ever set, 300 8-foot-wide helium balloons lifted a whole 4,335-pound house into the sky! We hope the owners weren't in there...