No, a lost balloon will not rise forever. A helium-filled balloon floats up and away if you let go of the string. But the balloon won’t keep on rising forever. The balloon rises because the helium (gas) inside it is lighter than the surrounding air.
A lost balloon will never rise forever. It will rise above the Earth until it reaches that height where the air is nearly as thin and light as the gas inside the balloon. At this point, the balloon will stop rising and will float along on the air currents.
Gradually, however, the gas that lifted the balloon will leak out, right through the rubber itself, and the deflated balloon will fall down to the ground.
Here are a few more facts about balloons and helium:
Foil balloons last for 3 to 5 days – sometimes longer as the technology as improved in recent years. They can be refilled by taking them to your nearest helium balloon retailer.
Latex balloons filled with helium typically float for only 8 to 12 hours. The gas escapes through small pores in the latex. Treated with Hi-Float – a glue like gel that makes the latex less porous and helps lock the helium in, they will last for over a week.
Helium gas is sensitive to extreme temperature changes. This means that:
Helium balloons might appear deflated in cold air – to resolve the problem, simply put your balloon somewhere warm and it will expand again.
You need to remember to keep your balloon away from extreme heat however, as this could cause the helium to expand and the balloon to burst.
Always keep the weight attached to the balloon to prevent it from floating away.
Content for this question contributed by Christopher Hite, resident of Elsemere, Kenton County, Kentucky, USA