I doubt it, too. Down and fleece work by trapping air so it can't move around as much, which reduces heat loss. Air free to circulate goes from the warm side, absorbs heat, moves to the cold side, and releases the heat to the other size. This is why vacuum bottles are such a great thing - no air means no convection or conduction.

I believe argon has about 2/3 the heat capacity of dry air, so it would be a little better, in the same way steel doesn't conduct heat as well as copper.

All that said, it's a pocket sized thing where a fleece or down vest is not. I knew I saw it somewhere...here's a link for sale, and a review:

http://www.bepreparedtosurvive.com/ProtectionProducts.htm

I have no connection to the site, but have read from someone on here that it's reputable.