They are usually (though not always) unmanned, filled with a lighter-than-air gas like helium, and fly at high altitudes.

These trees manufacture lighter-than-air gases which keep their upper branches buoyant.

We will fill them with my lighter-than-air gas.

I will need the power in my razor to help make the lighter-than-air gas.

Given the option 1 the jet will become a balloon filled with a lighter-than-air gas.

The lighter-than-air gas reduces his weight and allows him to fly surprisingly fast for a creature of his size.

As the bomb-shaped balloon filled with the lighter-than-air gas, the two men faced it into the wind.

It's a kind of sponge that produces a lighter-than-air gas.

Because the one with lighter-than-air gas filled inside of it would float if it was enough, or descend very slowly.

An aerostat is an aircraft that remains aloft through the use of lighter-than-air gases.