To make a very long distance flight, it is recommended to use a particular and really exceptional type of balloon: a Rozière. This aircraft takes its name from its creator Jean-François Pilâtre de Rozier (1785). The system has been improved since the 1990s by the British Don Cameron. In its modern version, this is a double envelope, containing the first, a gas lighter than air (helium) and the second, the hot air.
The advantage of combining helium /hot air resides in the fact that, in the evening, instead of unboarding ballast (principle of gas balloon) to slow the descent of the balloon due to cooling of the envelope, burners may be used to stabilize the balloon altitude by warming the chamber of helium. Finally, a Rozière floats thanks warming rays of the sun during the day and maintains its altitude, with the burners, in the evening and at night.
The great similarity between the gas balloon, the hot-air balloon and the rozière is that you never know when you take off, ever how long it will last, and much less where you will land.
The rozière primary application is for records and extremely long duration flights such as the first successful non-stop round the world balloon flight.
Rozière is pretty more complicate to manoeuvre than other traditional balloons.
Reference Pilâtre de Rozier Organisation – Collector 2011