Rozière balloon

A Rozière balloon (or simply Rozière) is a type of hybrid balloon that has separate chambers for a non-heated lifting gas (such as hydrogen or helium) as well as for a heated lifting gas (as used in a hot air balloon or Montgolfière). The design was created by Jean-François Pilâtre de Rozier (1754–1785).

A Rozière-type balloon has the advantage of partial control of buoyancy with much less use of fuel than a typical hot air balloon. This reduction of fuel consumption has allowed Rozière balloons and their crew to achieve very long flight times, as much as several days or even weeks.