I.e. nights where it’s too hot to be completely under the blanket but too cold to be without a blanket but having a limb covered keeps your whole body warm.
In: Biology
Imagine a house. It’s cold ASF, so you turn on a heater that’s located in a different part of the house. Eventually, the warmth from the heater will spread throughout the house.
When you put a blanket on your leg, your blood circulates around your body spreading the warmness. So it goes from your leg, eventually going to your thigh, then hips, then yada yada.
I can’t say for sure, but I would think the fact that your blood is constantly circulating around your body would transfer the heat from one side to the other?
The bottom of your feet and your palms are the only external part of your body without hair. Hair are used by the body as a natural form of insulation by being raised when we are cold trapping the air beneath them. This is why your feet get so cold and your palms are sweaty, knees weak, arms are heavy. There’s vomit on your sweater already, mom’s spaghetti
The point is that the majority (>60%) of the body’s heat is maintained through our feet, which is why they rub your legs first if you are ever frostbitten.
Try thinking about why you have to cover or uncover your legs to feel warmer or cooler.
Your body produces heat when it metabolizes food and does stuff that keeps you alive. On average it is around 100 W. The heat spreads in your body both by conduction and by pumping blood around. The blood flow can be regulated so if you get too cold less blood flows to your limbs and the core stays warmer, if you overheat more blood flows to the skin so it gets warmer and loses heat faster.
Heat leaves your body from the surface, and the rate depends on the temperature difference between the skin and what is beside it. What is beside is typically air but it can alos be the ground or anything else. The rate heat is transferred alos depends on what is between you and it, that will be clothes, blankets, etc.
It is the total heat flow that matters, if a blanket covers a limb it will reduce the rate heat is lost from that limb because the heat is distributed around your body just adding some insulation on one part can be enough so all of your body gets warm enough.
The rate you lose heat depends on the surface area, and your limbs are a surprisingly large part of it. A bit simplified is your head, left arm, and right arm 9% of the body area each. Your right leg and your left leg are around 18% each and your torso is around 18% on the front and 18% on the back the remaining 1% is the genital area. The exact percentage will depend on the person but it it a good way to get an idea of the area
So if you cover an arm with a blanket you have to reduce the rate heat is lost from about 9% of your body. It it was a leg it is 18% So it is not an insignificant amount of heat loss reduction. If that reduction is enough for your body to remain at a comfortable temperature that is enough
Think of clothes, blankets, etc, not as something that keeps you warm but something that stops the heat you produce yourself from escaping.
Covering our bodies “warms” us not by transferring heat *into* us, but by keeping body heat from escaping. So when you cover a part of your body, that part will lose less heat, reducing the overall loss of heat from your body to the environment, which results in feeling a bit warmer. Depending on the environment, that can be enough.
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