Really, I always figured that so long as the captive air didn't have an efficient means of conductive heat loss to ambient, it would retain it's insulating characteristics. I am also thinking that the reflective reabsorption from the outer layer will make the air chambers virtually effective insulators.

Now if the outer layer were wet cloth, I would expect that the vest would be worthless, as the thermocouple to ambient would be way too efficient.

One would think that, given it's construction characteristics, the thermocouple from the body side of the vest would be very efficient in comparison, thus allowing for a much higher entropy because the air in the chambers is captive and the weak thermocouple doesn't promote any closed cell loss.

In an open cell environment, such as sleeping bags or breathable down vests, the 1/8" captivity seems much more realistic. Loft becomes a factor because air movement is restricted/diminished due to macropore resistance which limits convective air flow, but in a closed cell system, I always figured the lack of any air flow fairly negated any convective heat transfer to ambient, except for a negligible amount due to the skin effect of the structure itself.

Kinda like when I stuff myself into one of them emergency survival bags and bind up the opening real good, leaving just a breathing tube sticking out, then proceed to overheat in about 3 minutes.