What element is used in some balloons?
Helium is much lighter than air, and thus a helium balloon is buoyant in air; though as He is a smaller particle than those of air the balloons deflate quicker.
As an added bonus, you can take helium balloons, purge your lungs with them by breathing the contents in and out, and then speak with a funny falsetto voice. Why are you not at risk being poisoned by helium gas?
Hot air balloonists simply use normal air, and heat up the insides of a balloon with a gas furnace. Because the hot air occupies much more volume than cold air, a buoyancy effect can be achieved.