For me there is a direct correlation between the flames of the campfire and my sleeping bag. They both take the chill off eventually, but not completely. As my front or backside reflects the fire it warms either my face or my posterior. My mummy bag encases almost all of me, to the exclusion of my nose. My nares get to inhale the chilled air. The fire and the bag do there best, it's just not perfect.
I try to stay warm before I turn in for the night. Conserve body heat. Fire the furnace. Think hot thoughts. That old camping prayer comes to mind. Now I lay me down to doze, I pray the lord my feet aren't froze. If I'm frozen, as I quiver, I pray the lord to stop my shivers. I always wake with, Blessed are the morning fire makers, they shall feel the heat. Wonder how hot Hades gets?
The old adage about cutting wood warming you twice is nice, until you quit splitting the stuff or standing by the fire you have to tend. Human Energy expended, is not directly related to the Btu's the fire emits. I quit splitting and eventually the fire dies down. It gets cold, I get cold.
My favorite is when anyone walks up and I'm vibrating in place.
You cold? Yeah I'm fra, fra, freezing. I'm usually too cold to say hypo something is settling in. Hypothermia is the wrong word for slowly getting teeth chattering cold. I can verbally get out its frigging cold, or it's colder than a witches, then I get a brain freeze. So I go to cot, hopefully not to clot.
When I wake up I fiddle to find my socks and reheat those which hold my toes. Adding Caffeine is like stirring the coals to my insides with fresh coffee. But to protect my digits I have to have gloves on for the mornings chill and the hot of the coffee cup.
At breakfast I ache for the sunshine like a snapping turtle does a sunny log.
I am warm blooded. The turtle is cold blooded. We both savor soaking the same sun. I have never had a turtle, turtle its way up to my campfire, so I know those snappers got something in there shell I want.
Getting warm and staying warm is at times an effort to be sure. Ah, but me being blessed by the Irish I've hit upon the cure. Lasting internal warmth of earthy blood flowing warmth. If the sun wont shine outside, I make it burn brightly inside.
From my thermos The Irish cream works its spirits out of the bottle and into my being. Blessed be the breakfast that follows. I can hoist a toast and toast my insides. The warmth oozes through me. Then I don't feel the backside chill of the campfire. Suddenly my coffee is not mouth burning hot, and the stove of my insides is brewing nicely.