| | 0 lb, 0 kg |- | | | | |- | | | | |} The density of air at is about . The total lift for a balloon of heated to would be . This is just enough to generate neutral buoyancy for the total system mass (not including the heated air trapped in the envelope, of course) stated in the previous section. Liftoff would require a slightly greater temperature, depending on the desired rate of climb. In reality, the air contained in the envelope is not all at the same temperature, as the accompanying thermal image shows, and so these calculations are based on averages. For typical atmospheric conditions (), a hot air balloon heated to requires about 3.91 m3 of envelope volume to lift 1 kilogram (equivalently, 62.5 cu ft/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above sea level, and humidity of the air surrounding. On a warm day, a balloon cannot lift as much as on a cool day, because the temperature required for launch will exceed the maximum sustainable for nylon envelope fabric. Also, in the lower atmosphere, the lift provided by a hot air balloon decreases about 3% per 1,000 m (1% per 1,000 ft) of altitude gained. Montgolfier Standard hot air balloons are known as Montgolfier balloons and rely solely on the buoyancy of hot air provided by the burner and contained by the envelope. This style of balloon was developed by the Montgolfier brothers and had its first public demonstration on 4 June 1783 with an unmanned flight lasting 10 minutes, followed later that year with manned flights. Hybrid The 1785 Rozière balloon, a type of hybrid balloon, named after its creator, Jean-François Pilâtre de Rozier, has a separate cell for a lighter-than-air gas (typically helium), as well as a cone below for hot air (as is used in a hot air balloon) to heat the helium at night. Hydrogen gas was used in the very early stages of development, but was quickly abandoned due to the danger of introducing an open flame near the gas. All modern Roziere balloons now use helium as a lifting gas. Solar Solar balloons are hot air balloons that use just solar energy captured by a dark envelope to heat the air inside. Steering Hot air balloon can be steered