Hot air balloons work thanks to the difference in density of the air inside the balloon with respect to the air outside. Inside the balloon there is usually helium or hot air, both of which are less dense than the outside air.The height that hot air balloons reach will depend on the density of the air inside the balloon, since once this is leveled with the outer density, the balloon will stop rising. To descend, the density of the air in the balloon must be greater than that of the air outside. This handling of densities is the task of the balloon pilot...Discover more in this podcast.