Almost every source I can find online maintains that two 0.5 cm blankets are significantly warmer than a single 1cm blanket due to air trapped between the thin blankets.
However, the thermal conductivities of air and wool are roughly comparable according to this website. That would seem to mean that air only aids the insulation significantly if the thickness of the air layer is significant compared to the thickness of the blankets, which I would guess it is not.
Further, in order for heat transfer through the air to be dominated by conduction, the air needs to be extremely still, which it seems it would not be around a living, breathing, human. Otherwise the air would mix and not provide significant insulation.
Is there any empirical evidence that two thin blankets are superior? If so, why is that, given the above considerations?