So the hair stands up. This is said to create more insulation That makes no sense Yes, the hair stands up, making the barrier to your skin greater. But before it was standing up, it was laying flat, covering all of your skin. When it stands up, it leaves more of your skin exposed, because it was covering the whole surface area, and now it is covering less of the surface area, but a higher length. Wouldn't these effects just cancel each other out?

The insulating effect is caused by the air that's trapped between the hair. When it stands up it traps more air than when it's lying flat.

Piloerection works better if the hair is longer, which it used to be on humans. When the longer hairs stand on end, they trap air which is warmed by the skin to provide an insulative barrier. It's the same effect as being colder in pants that fit tightly to your skin as opposed to pants that are looser and allow for air to be trapped and warmed by the body, from what I've heard.

Well with looser pants there is actually more material then tighter pants. Wouldn't a better analogy be comparing tight pants that cover all of your skin to loose shorts?

 

When the hair is laying flat on your skin it is "tight" and covering all of your skin But when it is raised, although it is "looser", it is also covering less area

Well with looser pants there is actually more material then tighter pants. Wouldn't a better analogy be comparing tight pants that cover all of your skin to loose shorts?

 

When the hair is laying flat on your skin it is "tight" and covering all of your skin But when it is raised, although it is "looser", it is also covering less area

 

But as Phi For All said it used to be useful for humans. When we had longer hair. I think the theory is that it just never stopped happening, since when people had longer hair on their bodies. It's become redundant in a sense.

Well with looser pants there is actually more material then tighter pants. Wouldn't a better analogy be comparing tight pants that cover all of your skin to loose shorts?

 

When the hair is laying flat on your skin it is "tight" and covering all of your skin But when it is raised, although it is "looser", it is also covering less area

 

No this is an example of surface area to volume ratio, one example would be why whales have grown to the size they have or another would be the Eskimo (short and fat increases this ratio). The conductive property of air, isn't all that good, so trapping air between hairs is a way of increasing this ratio without the need to increase subcutaneous fat, which requires a lot of excess energy, which is hard to come by and we humans need the extra energy for our huge, relative to size, brains.

Edited August 18, 201213 yr by dimreepr

Well with looser pants there is actually more material then tighter pants. Wouldn't a better analogy be comparing tight pants that cover all of your skin to loose shorts?

 

When the hair is laying flat on your skin it is "tight" and covering all of your skin But when it is raised, although it is "looser", it is also covering less area

But your analogy assumes that more material means "warmer". And if so, how do you explain why the Bedouin wear layers of loose clothing to stay cool in the desert heat? It's the trapped air again, being cooled this time by perspiration, acting as insulation against the heat.

 

Piloerection isn't just for insulation either. It's an arousal response, and it can happen when you get scared or angry. Again, when we had longer hair, this actually made us look bigger.

 

It's used by many mammals for defense. It's actually what makes a porcupines quills stand up in response to danger.

Edited August 19, 201213 yr by Phi for All
correction

I understand now, thanks. Now I am wondering though....how does the hair 'trap' the warm air?

I understand now, thanks. Now I am wondering though....how does the hair 'trap' the warm air?

Hair and fur basically block air currents from stripping away air heated by the body. The hair creates a more or less motionless area where the air can be thermoregulated.

Got it, thanks!