Longest duration balloon flight (overall)

The longest time a balloon has stayed aloft is 31 days 20 hours, by an unmanned NASA scientific balloon over the South Pole between 20 December 2001 and 21 January 2002. The giant helium-filled balloon, made of polythene material about the thickness of plastic sandwich wrap (0.002 mm), expended to a diameter of more than 129 m (424 ft) as it climbed to an altitude of around 38 km (23.6 miles). Its size enabled it to carry the two-tonne (4,400 lb) NASA Tiger (Trans-Iron Galactic Element Recorder) experiment around the South Pole twice, covering a distance of 14,000 km (8,800 miles).