A striped balloon drifts gently over rolling hills and a winding river, kept aloft purely by the ideal gas law: a propane burner heats the air inside the envelope to around 100°C, making it roughly 25% less dense than the cool air outside so buoyancy lifts the whole rig. Real envelopes hold about 2,000-3,000 cubic meters of air, and a good burn can produce a climb rate of 1-5 m/s. Pilots steer only by altitude — rising or descending into different wind layers — since balloons have no direct horizontal propulsion, they simply ride the breeze.