A hot air balloon is a type of aircraft that uses a large, colorful envelope filled with heated air to lift off the ground. The hot air inside the envelope is less dense than the cooler air outside, allowing the balloon to rise. A burner, fueled by propane, heats the air, and the pilot can control the altitude by adjusting the temperature. Hot air balloons are often used for recreational purposes, offering scenic views during flights. They are typically made of nylon or polyester fabric and can carry passengers in a basket attached to the envelope. Balloon festivals are popular events where multiple balloons take to the sky, creating a vibrant display.