"All body surface area is not equal
Head is more important than torso than arms and legs
If you're cold, reduced blood flow to arms and legs will cool them off, so there will be less heat leaking out there"
I have been thinking about this thread a lot while training in the cold rain these past days.
I have to agree with the above statement. Even though the head has a relativeley small BSA it is responsible for a very much greater amount of heat loss due to the blood flow very near the surface of the skin.
When it comes to being comfortable I and quite a few of my friends(judging by the insulating garments they wear) have found that keeping the Torso, Head, Hands ,Feet, arms, and legs warm in that order of importance to yield the best results.
If someone locked me in a meat locker naked and offered me one piece of clothing at a time I might chose differently say: Torso,feet,head,hands,arms,legs due to percieved immediate comfort.
Either way the head is very much more important to preserving heat than it's 4% BSA would indicate.
I have to add though that i am tentatively on board with the CLO ratings VS simple measures of loft in regards to warmth.
I recently added an MLD spirit quilt with APEX insulation to my gear and have been testing it alongside my WM ulta-light down bag.
The 1.75" of measured loft of my APEX is as warm as the 2.5" measured of Goose down loft.
I used them both as a quilt at temperatures from 38 degrees to the low 50's. At least in my subjective determination they are equally as warm.
The other factor is the momentum fabric of the MLD quilt has greater warmth to the touch. It even seems to warm up quicker but this could be due to the lack of quilting that allows less dead airspace than my down bag.
I was about as stubborn a "loft is warmth" guy as there ever was but lately my experience with APEX is changing my mind.