[Tossrock]

I assume they meant that if you were to double the diameter of the balloon, it would be a superlinear increase in lifting capacity (since volume is cubic in radius). However, it wouldn't actually be exponential, and two balloons added together definitely does not equal more than the sum of their individual lift capacity.

[jackcarter]

To be precise, it's 8x the lifting capacity (=2^3), which would be 5.6 million tons, or "nearly 6 million".

[kissickas]

OK, so just the journalist misunderstood then? Because doubling the diameter is in no way compatible with "add a second balloon."