Gas balloon

A gas balloon is a kind of balloon that uses a gas of low density to fly using buoyancy. Gas balloons sometimes fly very high, very far, and for a very long time.
A gas balloon is different from a hot air balloon. A hot air balloon uses a fire to lower
the density of air. A gas balloon does not use fire.
The most common use for gas balloons are to measure the atmosphere. These are called weather balloons.
Some gas balloons carry people.