Hot Air Balloons are lighter than air when filled
with helium. These are known as aerostats, or lighter than air
crafts.
Balloons today are made with nylon or light plastic. It is usually
filled with helium or hydrogen. These gases are heated with a
burner. This makes the balloon rise. When in the air you can't
steer the balloon, the wind blows in a direction.
The passengers and pilot ride in a large basket called the cockpit
suspended from the balloon.
Today balloons are used with tools to measure air temperature,
air pressure, and moisture.