I came across the following picture on a news site, in a series of 'this day in...' type items.
The accompanying text reads (in Dutch)
22 juni 1975 - In Geldrop werd de Internationale Holland Ballonwedstrijd gehouden. Deelnemers uit zeven landen streden daar om de Trophee du ballon libre.
Which translates to
22 June 1975 - The International Holland Balloon competition was held in Geldrop. Contestants from seven countries competed for the Trophee du ballon libre.
To my surprise, the balloons are round and are closed at the bottom. What type of balloons are these? They don't seem to be hot air balloons, are they?