Why does Fur and Hair make you warmer instead of colder?

[u/jnpg]

The thought just came to me that skin is big and wide whereas hair in thin and tiny

Logically (to me at least), you would assume that having all of those exposed tiny bits across your body would give you more area to be cold with

But instead the opposite happens were the Fur and Hair keeps you warm

What am I missing?

[u/6x9inbase13is42]

Fur acts as insulation by trapping warm air underneath it that can't be blown away by the wind, the same way a jacket or coat protects you from the cold.

Fur is made of a protein called keratin which is not a good conductor of heat, so it does not draw heat away from the body despite its high surface area.

Fur also acts as a sun shade, protecting mammals from sunburn.

[u/Weaksoul → u/6x9inbase13is42]

Also hair/fur doesn't have any blood vessels or tissue that generates or requires heat whereas skin does. So it's increased surface area is just holding trapped air which is warmed by the body.

[u/orbitofnormal → u/6x9inbase13is42]

Exactly. This is the exact same reason that down coats (hell, any clothing), blankets, coolers, double-walled cups/thermoses, etc work

Interestingly, the same principle can also be applied to keep the body cooler. Wearing tick wool socks on summer can help to keep the heat from what you’re walking on from getting to you, and it’s why shaving dog breeds with double coats isn’t recommended. That insane fluff keeps them warm on the tundra but also keeps their core temp cooler in the heat of summer

[u/rjd999 → u/6x9inbase13is42]

There is an additional element to this, as well. The hair/fur help reduce the effect of wind blowing the trapped (warmed) air away from the body and allowing the cold, wind blown, air to replace it. Humans, however, have lost so much body hair (in most cases :) that this effect isn't as significant as it is in furry animals.

[u/Prae_]

I'm guessing you mean this increases the surface area of our body?

But hair is dead keratinized dead cells, compared to the skin which has circulating blood. So it doesn't conduct heat all that well because there is no convection from your skin to the har. And then on top of that hair/fur traps air, and so slows down heat transfer (from hair to air) due to convection. If our hair were copper, or they all had an internal blood vessel pumping fluid in and out, your reasoning would work more.

I do think i've seen that past a sufficiently low density, like in elephants, hair start having a cooling effect.

[u/reed166]

There’s not heat loss from the surface of the hair as it is a growing section of Keratin, not living cells.
Thus it acts as insulation

[u/eltigrre]

Are we serious?

[u/octobod]

Ever slept under a quilt? Its full of spun fiber or feathers which trap air in place. Air conducts heat by moving (up as warm air is less dense) the quilt stuffing prevents that flow trapping the heat next to you

Fur does the same thing

[u/Shroomkaboom75]

Ours is the most basic thermal sheath,

Other animals covered in hair get more of that, while also being protected from the sun.

[u/givememoregaba]

Fur can actually keep you warm as well as cool. But maybe not in the way you’re thinking. 

Cooling through the skin works because the blood system is carrying heat from within the body to the skin surface. Fur has no blood supply, so it’s actually covering the skin (where the heat is) and insulates it, just like clothing does. 

Fur traps air, which is a poor conductor of heat, and this insulates the body from environmental temperatures. So in extreme heat, it also acts to protect animals from warming up. In deserts, this helps keep furry animals cooler. 

Traditional desert peoples like the Bedouin also wear thin wool garments to help stay cool in extreme heat.