Why does CO2 permeate balloon material faster than air despite higher molecular weight?

[PAllen]

So, doing an experiment with my daughter (making similar size balloons filled with carbon dioxide and air), and verifying that the CO2 balloon fell quite noticeably faster due to higher molecular weight; I later noticed that the CO2 balloon shrank clearly faster than the air balloon. This was quite a surprise because CO2 is 'bigger' by weight and includes two oxygens. However, a little internet research found that permeability size is effectively the same as kinetic size, and that the size for permeability of the following molecules is exactly the inverse of their molecular weights: N2 'bigger' than O2, which is 'bigger' than CO2. For me quite a surprise, but also doubling of the value of the experiment.

 

[mitochan]

You teach me that CO2 molecule is made of three atoms and smaller in size than O2 which is made of two O atoms with no C. Interesting!

 

[Borek]

Carbon dioxide is known to easily "dissolve" in rubbers.

 

[256bits]

You teach me that CO2 molecule is made of three atoms and smaller in size than O2 which is made of two O atoms with no C. Interesting!

CO2 is a linear molecule, with C and O sharing electrons, maybe more towards the C.

And CO is even bigger than CO2.
Interesting indeed!

But they do say to pump up yours with N2.