How does a hot air balloon fly?

Basically, hot air balloons use the basic scientific principle that warm air rises in cooler air.

The air is held in the 'balloon envelope' which is usually made from polyester or nylon fabric (similair to parachutes). Underneath the envelope is the balloon's burner which is fueled by propane gas to heat up the air and mae the balloon rise.

There is also a valve at the top of the balloon to help to control the height of the balloon.