Hot air balloons fly by Archimedes' buoyancy principle: heating the air inside the envelope makes it less dense than the cooler air outside, so the balloon's weight is offset by the upward push of the surrounding, denser air it displaces. The pilot controls altitude almost entirely with a propane burner that reheats the air — firing it raises temperature and lift, easing off lets the air cool and the balloon sink — and can also vent hot air out the top parachute valve for a faster descent. Because the whole envelope moves with the wind around it, balloons cannot steer sideways; pilots instead climb or descend to catch different wind layers that are blowing in the direction they want to travel. This makes ballooning a activity acutely dependent on calm, predictable weather, which is why most flights launch at dawn or dusk when winds are lightest. The first untethered manned flight was made by the Montgolfier brothers in Annonay and Paris, France, in 1783, using a paper-and-fabric balloon heated by a straw fire.

• Typical envelope volume: 2,000–3,000 m³ (some sport balloons under 1,000 m³, giants over 5,500 m³)
• Air inside the envelope is heated to roughly 100°C, versus ~15–25°C ambient air outside
• Propane burners produce roughly 1–3 million BTU/hour of heat output
• Typical cruising altitude for sightseeing flights: 300–900 m (1,000–3,000 ft) above ground
• Typical ascent/descent rates: 60–150 m per minute (200–500 ft/min) under normal control
• Balloons have no horizontal steering — pilots change altitude to ride different wind directions
• The Montgolfier brothers' first public untethered flight was June 4, 1783, near Annonay, France
• A typical flight lasts about 1 hour and covers roughly 8–15 km depending on wind speed