The idea is you fill them with helium, and (let's say) someone is 41 years old, you simply buy a 4 and a 1 and fill them both with helium, and they say 41.
They also do letters of the alphabet (shown in the picture).
Here's the question:
Which letter or number is it safe to assume has the largest internal volume for helium?
In other words, which single letter or number would I pick if I wanted maximum "floatyness"?
