A hot air balloon is an aerostat that utilizes the principle of buoyancy to achieve lift. The device operates by heating the large envelope, causing the internal air mass to expand and reach a temperature that makes it less dense than the cooler ambient air surrounding it. This density difference creates a net buoyant force, allowing the structure to rise. The structural integrity is maintained by durable fabrics, while the heat source provides the necessary thermal energy. Altitude and descent are controlled by modulating the heat input to manage the volume and temperature difference required for lift. This technology serves as a method of atmospheric transport, relying entirely on basic principles of thermodynamics and fluid dynamics.