[dbcdbc]

Years ago, I inflated some latex party balloons with freon12. They're so heavy that you can throw them across the room, and they just land on the floor and stay put.
But the surprise is that they go flat in about two hours!! Last time I went to school, freon molecules were much larger than helium atoms, and don't behave as bosons, besides. How do they escape the balloon so quickly?? 

[billnotgatez]

If you inflate again a balloon that has gone flat from freon does it deflate again at the same rate?

[billnotgatez]

Just a FYI based on a GOOGLE

1.225 kg/m^3
According to the International Standard Atmosphere (ISA) values—15° C at sea level—the density of dry air is at: In Metric units: 1.225 kg/m^3. In Imperial units: 0.0765 lb/ft^3

From WIKI

Dichlorodifluoromethane (R-12) is a colorless gas usually sold under the brand name Freon-12
Density   1.486 g/cm3 (−29.8 °C (−21.6 °F))

[Borek]

Rate of deflation depends on the permeability of the membrane, which in turn depends on many factors. One of the them is solubility of the gas in the membrane material - and while you are right that size of the molecule matters, there are many other factors involving interactions between molecules of the gas and molecules of the membrane. Helium is quite bad at these interactions, its high diffusion rate in most materials stems from small size, apparently that's not always enough to beat the speed record.

[dbcdbc]

@billnotgatez:

I never tried reinflating any, as I tied them shut in the usual manner, which is pretty nearly impossible to undo.

@Borek:

Yes, possibly the interaction requires a very slight van der Waals force that helps align the molecule in pores in the latex, yet isn't strong enough to keep it pinned in place. I'm sure chlorofluorocarbons mostly exhibit slight van der Waals forces, and CCl₂F₂ is a fairly compact spheroid.

[Enthalpy]

Or rather, some freon reacts chemically with the rubber, essentially destroying it, and then the remaining freon leaks easily.

Any chance for a Kharasch addition? We don't have exactly a CXCl₃ here, but the reaction has been observed for other reactants, and rubber is full of double bonds.
https://en.wikipedia.org/wiki/Kharasch_addition
The addition proceeds at room temperature, light helps.

While freons are little reactive, I already spent hours trying to clean aluminium parts with a freon, and my rags stayed dirty indefinitely - until the provider explained me that freons oxidise aluminium.