It seems to me from my reading and no actual experience with the material (yet, I have some on order) that IX works more or less the way thermal windows (or double pane windows work) the air is in a dead space acting as an insulator. Air that does not move is a very good insulator. Is this not how down works? It traps air when it is at full loft creating essentially a dead air pocket within the down.
I am not an expert on insulation , "but I did stay at a Holiday Inn Express last night."
(I really am not an expert I am just trying to remember high school physical science.)