  Balloon releases are one of the main attractions of many fairs. Helium filled
rubber balloons are released to carry postcards over preferably long distances.
Although such balloons have been considered in atmospheric sciences and air
safety analysis, there is only scarce literature available on the subject. This
work intends to close this gap by providing a comprehensive theoretical
overview and a thorough analysis of real-life data. All relevant physical
properties of a rubber balloon are carefully modelled and supplemented by
weather observations to form a self-contained trajectory simulation tool. The
analysis of diverse balloon releases provided detailed insight into the flight
dynamics and potential optimisations. Helium balloons are found to reach
routinely altitudes above 10 km. Under optimal conditions, they could stay more
than 24 hours airborne while reaching flight distances close to 3000 km.
However, external weather effects reduce the typical lifetime to 2-5 hours.
