We can pumped gas into the balloon such as helium, hydrogen, oxygen, nitrous oxide (laughing gas) , and air
but helium is safer because it nonflammable.
Although helium gas was expensive than hydrogen and other , it worth for asset and security of life.
A balloon sky that filled with gas is lighter than air, that can make it rise up in the air.
When I was young I really like to look up to the sky and try to found balloons,
when it float and combine it is very beautiful.
All of the picture are impressive and worth remembering!!