[dfox]

Originally Posted by JeffM

I'd rather sweat than bleed - any day. I'm ATGATT even in hot weather.

When it is really hot, you cannot sweat fast enough to cool yourself and wearing mesh, or less, does not cut it. It sounds counter intuitive but you heat faster with mesh or less. At that point you must insulate.

Good reading here from the Ironbutt folks:

http://www.ironbutt.com/ibmagazine/i..._62-66_Hot.pdf



Or from the master, David Hough: http://www.soundrider.com/archive/sa..._youre_hot.htm

While I appreciate the knowledge that these folks are trying to expel, their reasoning is misleading and false. It' not high temperatures that prevent our bodies from cooling, it's high humidity. Our bodies can survive temperatures much higher than 100 as long as the relative humidity isn't too high.

On a day above 90 degrees, your body relies solely on evaporative cooling to maintain a temperature, not convective cooling. There is no other method, aside from consuming something cold. That's why you sweat even when doing nothing. As each water molecule from sweat evaporates from our skin, it takes heat away from our body, and cools us. Evaporative cooling only works when there is capacity for additional moisture in the air. As the air reaches 100% relative humidity, there is no more cooling left. That's why, on a 90 degree but 100% relative humidity day, it feels a lot hotter than a day that's 100 degrees but only 60% relative humidity. You're body can't cool itself once the relative humidity reaches 100%.

Now, if we seal up our jackets and avoid providing fresh air into our jackets, we are effectively getting rid of the only method of cooling that our bodies have. After just a few short minutes, the air within the jacket will reach 100% humidity, and our sweat will no longer evaporate. Our body temperature will continue to climb, until it reaches equilibrium with the exterior temperature. The only way to continue to cool yourself, is to refresh the air in your jacket with air that is not at 100% relative humidity. These folks might not realize it, but they're getting some air change in their "sealed up" gear, and that's the only thing that's cooling them down.

Desert nomads wear long clothing to keep the sun off their skin. The clothing is loose and open. This allows for constant refreshing of the air that's within the clothing, continuing the process of evaporative cooling.


So, bottom line is, if the relative humidity isn't 100% outside, you need MORE AIR ON YOUR SKIN. Once it reaches 100% relative humidity, well then, there's really nothing you can do, because your body has no way to cool itself.

and don't even get me started on "moisture wicking" clothes keeping you cool. That **** is only good for one thing, and that's to keep you from stinking, preventing swampass, and avoiding blisters on your feet.. Moisture wicking clothes pull the moisture away from your body before it has the chance to evaporate - again negating evaporative cooling.

/mechanical engineering discussion.