How can I blow up a balloon more (once sealed) without adding any more air?

Question

How would you blow it up more without adding any more air? You can't add anything like helium, water, etc. and it's already sealed. I think it has something to do with heating and cooling or something...

Answer 1

There are two ways:

1) Heat the balloon.
2) Decrease the pressure outside the balloon.

Answer 2

You need to put the ballon in a vacuum chamber and suck out the air, that will lower the pressure around the ballon and it will expand.

Answer 3

Heat it and the gas in it. Take it to a higher altitude, where the pressure is lower.