What gas do you put in balloons?

Answer 1

Ordinary air can be used to fill balloons, but they will not float or lift anything. You would need to add a gas that is lighter than the nitrogen or oxygen that makes up most of air, and one that is light enough to lift the weight of the balloon.

Today, we typically use helium gas (atomic number 2) which is light, non-reacting, and non-polluting. It is only about as dense as normal air found at several miles above the Earth. Weather balloons and advertising blimps use helium.

You could also use hydrogen gas, which is plentiful and cheaper, but it is flammable or explosive when mixed with oxygen and ignited (as by a spark). Early German passenger dirigibles used hydrogen, and a famous one, the Hindenburg, was destroyed by fire when visiting the US in 1937.

The large hot-air balloons that float and race are lifted by heated air, which is less dense than the same volume of cooler air. Using flame burners, the hot-air balloons can maintain their lift until their supply of fuel is gone. Almost none have the capacity for directed flight, and move with the prevailing winds.

Answer 2

Helium is commonly used to inflate balloons because it is lighter than air, allowing the balloon to float. Some balloons may also be filled with air, especially if they are small or decorative balloons.