Why can't foil balloons fly after being inflated?

The core reason why the bought foil balloon cannot be lifted off is that the density of the filling gas is not lower than that of the air, which makes the balloon unable to gain upward buoyancy.Wrong selection of 1. inflation gas (main reason)

1. Incorrect filling of "air": the gas blown out by the air pump and mouth is all air (density is about 1.29 kg/m),

After inflation, the overall density (including the weight of gas and foil balloon) is greater than or equal to the air density, so it does not produce buoyancy and cannot float naturally.

No "light gas" is selected: the only gas that can make the foil balloon float is helium (density is about 0.18 kg/m) or hydrogen (density is about 0.09 kg/m), of which helium is safer (hydrogen is flammable and explosive, and is not recommend for non-professionals).

2. Foil balloon its own weight or air leakage affects buoyancy

Even if filled with helium/hydrogen, if the balloon itself is too heavy or leaks, it will offset the buoyancy.

Balloon weight exceeds the standard: some fancy large-size foil balloon, thick material foil balloon (such as with complex decoration, three-dimensional shape), their own weight is relatively large, if the amount of light gas filled is insufficient, the balloon will also be unable to float.

The balloon has air leakage phenomenon: when buying foil balloons, there are small cracks, the heat sealing at the joints is not tight, and the light gas leaks slowly, resulting in the internal gas density gradually approaching the air, the buoyancy weakens until it disappears, and the balloon sinks (it can float just after filling, but does not float for a period of time, most of which are air leakage problems).

3. Insufficient aeration or environmental factors (secondary causes)

Too little inflation: the amount of light gas filled is not enough, the volume of gas inside the foil balloon is small, and the buoyancy generated is not enough to resist the weight of the foil balloon itself. It needs to be filled until the balloon is fully expanded but not tightly supported, and the buoyancy is enough to make the balloon float in the air.

Low ambient air density: the air density in high altitude areas is slightly lower, even if the use of light gas, there will be the problem of balloons not floating in the air.