I've spent a fair amount of time avoiding hypothermia, but I'm not qualified to say much about treating it. There are different stages, and at the stages where the body is just losing heat faster than it can generate it, anything will help- insulation, reflection, shelter.

My understanding, though, is that at later stages the actual capability of the body to generate heat is compromised, and it becomes much more difficult for the patient to recover just using mechanisms that work by retaining that body heat. If that's all you've got, then you do what you can, but the medical advice I've seen for severe hypothermia always seems to emphasize external sources of heat, as fast as possible (short of scalding/burning, of course).

But, as I say, I have no expertise in that area. Maybe adding to the subject line will counteract the thread drift and attract attention from those who do.

It's amazing how many facets of survival are just thermodynamics in disguise. If it weren't for the need to keep body heat up, we wouldn't be concerned about clothing, sleeping bags, tents and shelter, rain gear, making fires... almost everything we talk about is directly or indirectly about heat flow.