What hybrid balloon type combines hot air with a gas such as helium?

A Rozière balloon combines hot air with a lifting gas such as helium.

The design is named after Jean-François Pilâtre de Rozier, the French balloon pioneer. A Rozière has separate chambers: one contains a permanent lifting gas, while another contains air that can be heated. The gas provides continuous buoyancy, and the heated-air chamber allows the crew to adjust lift without releasing the main lifting gas.

This hybrid arrangement can support very long-duration flights. Gas balloons and hot-air balloons have different strengths: gas balloons can remain aloft efficiently, while hot-air balloons offer some control through heating. A Rozière attempts to combine those advantages, although it is technically demanding to design and operate.

Pilâtre de Rozier died in 1785 while attempting to cross the English Channel in an early balloon combining hydrogen and hot air. Modern Rozière balloons use safer engineering and have completed major long-distance missions, including successful circumnavigations of Earth.