Abstract: A hot air balloon vent for use with a thermal aircraft or hot air balloon is provided. An aperture associated with the aircraft or balloon is generally adapted to be closed by the vent which includes an operculum of a flexible material that is substantially of parachute form. A control mechanism is provided to effect closure of the aperture by extending the operculum laterally or radially. When so moved, the operculum may be extended to its maximum surface area, at which point it covers and seals the aperture. The control mechanism generally includes conjoined contiguous vent control elements that permit the outer perimeter of the operculum to be pulled away from the perimeter edge of the aperture to variably open the aperture.