The physics is simple. A helium balloon rises while the surrounding air is denser than the gas inside it, so indoors it goes straight to the ceiling and stays there until the helium leaks out and it comes down.
Outdoors there is no ceiling. As the balloon climbs, atmospheric pressure drops and the gas inside expands, stretching the envelope until it fails, which for a latex balloon usually happens somewhere in the range of several kilometres. A foil balloon may vent rather than shatter, but it too eventually falls. Wind, temperature and how tightly the balloon was filled all shift the exact altitude.
This is a physics answer rather than a suggestion. We do not carry out balloon releases and we advise clients against them, because everything that goes up comes back down as litter in the sea or the desert, where it harms wildlife, and because stray balloons are a recognised hazard around aircraft. For a dramatic moment we build indoor balloon drops instead, which give the same effect with nothing left behind.
- Indoors: the balloon rises to the ceiling and stays there
- Outdoors: it climbs until pressure drop expands it past bursting point
- Latex typically fails at an altitude measured in kilometres
- Everything released returns to the ground or the sea as litter
- We use indoor balloon drops instead of outdoor releases