Answer:
We can measure volumes approaching absolute zero and then predict what the volume would be at absolute zero.
Since there is NO molecular motion at absolute zero, the volume of a balloon at absolute zero should be zero.
If you headed to the deepest recesses of intergalactic space, shielded from starlight, the only thing that would heat you up would be the Big Bang's leftover glow: the cosmic microwave background at 2olume.ht v725 K. At that temperature, the balloon would have a volume.
