In reply to Si Withington:
I've just read the marketting blurb about Celliant. As a former propulsion engineer, I think its full of unsubstantiated waffle. In short, it sounds like "snake oil".
It talks about absorbing and reflecting infrared energy from the body. But the manufacturing description suggested it is a fibre with low emissivity, so it's going to simply reflect body heat back towards the occupant. There's going to be little absorption going on.
And in any case, if your skin temperature is 30 degs C and the inner layer of the garment is at 25, i doubt there'll be much interchange of radiant heat. It'll mostly be conduction and a bit of forced convection (caused by the occupant moving inside the garment).
Nowhere does it actually say how thick it is, or what it's thermal conductivity is. But that would give the game away.
Caveat emptor...
