The world's largest balloon ever clocked in at a volume of 30 million cubic feet. The balloon was, of course, sponsored by Red Bull. It's definitely an impressive size, but consider this: isn't the world's largest balloon actually everything in the universe that's not inside the world's smallest balloon? To put that in other words, imagine that the universe consisted of a Klein bottle made of latex. What's the inside of the balloon and what's the outside?
The world's smallest balloon was made with a special carbon membrane one atom thick, containing a volume of 300 cubic micrometers (approximately 1*10^-14 cubic feet of air). That means that the volume of the world's largest balloon is actually, to estimate very roughly with NASA's numbers, about ten trillion cubic light-years. Eat that, Red Bull.