How high will a helium balloon travel before it pops?
It will float (being lighter than air) until the pressure inside is so much greater than the pressure outside that the rubber that the balloon is made of can’t handle the strain anymore. That will depend on how strong the rubber is that the balloon is made of. Weak balloons will pop lower down, while strong balloons can rise very high indeed (like weather balloons). So it’s kind of hard to answer the question. Maybe one could make a reasonable set of assumptions and calculate when it would happen for a toy balloon. I read somewhere Weather balloons used by the National Weather Service upper air program are designed to go up to around 100,000 feet!!!.
