What makes hot air balloons come to mind?

When I looked at the hot air balloon, it wasn't blocked like a helium balloon, but it was pierced downward.

That doesn't mean you use helium as light as a helium balloon.

I think it's just heating it with a burner, what principle comes to mind?

1016 2016-04-26 Gentleman

Hot air balloons use the principle that hot air is lighter than cold air.
The air is heated in the burner under the hot air balloon, which fills the hot air balloon.
So the whole balloon comes to mind.