Moisture Wicking Shirts & The Desert?

Cotton is generally a bad material to wear in a survival situation. It's cheap, it breaths well and it feels great. But when you get sweat in the cold, it'll absorb that moisture and you'll pay for it when the temperature drops. 

But what about in the heat? 

When I go camping in the desert I usually wear a moisture wicking undershirt, as well as a synthetic shell shirt during the day, and then switch to thermal underwear at night. This of course depends on the temperature. The key here is that both shirts (the hot weather shirt and the thermal shirt) are constructed out of moisture wicking materials. 

Just as a refresher: sweat is our body's natural cooling mechanism. When we sweat, we lose heat in a few different ways. Primarily this is through evaporation, which acts as a refrigerating effect on the skin. Sweat in the heat is a good thing, it will cool you down. It's just important to make sure you dry up before the temperature drops. 

The moisture wicking t-shirts do the trick (the thermals also wick moisture away but this is to prevent freezing rather than facilitate cooling). I'm dry as a bone when rock climbing or even jogging in the heat. But when thinking about survival clothing, is a moisture wicking shirt the best idea? Or maybe this is the one situation where cotton might be beneficial? 

I'll explain why I'm questioning this. As a general rule, when water is limited in a hot location, you actually want to layer up. It sounds counter-intuitive, and in a way it is, as this will increase your body's temperature. But it will also prevent sweat from escaping as it gets trapped in your clothes. Here's a quote from the US Army's Survival Field Manual FM 21-76 p 135: 

Conserve your sweat. Wear your complete uniform to include T-shirt. Roll the sleeves down, cover your head, and protect your neck with a scarf or similar item. These steps will protect your body from hot-blowing winds and the direct rays of the sun. Your clothing will absorb your sweat, keeping it against your skin so that you gain its full cooling effect. By staying in the shade quietly, fully clothed, not talking, keeping your mouth closed, and breathing through your nose, your water requirement for survival drops dramatically.

The Army Combat Uniform is
the successor to the Battle
Dress Uniform (BDU). It's
standard wear for soldiers in the
middle east, where temperatures
can reach as high as 130 F. 

Essentially what the army is stating is that trapping the moisture in will increase the likelihood that some of it is re-absorbed by the skin. The skin is water resistant but to a point and it will absorb some of the moisture, although your sweat is heavily laden with salt...

The answer, as you see, is quite mirky. However the Army has a lot of experience with desert survival and I'm willing to go with their recommendation, particularly because the current Army Combat Uniform includes a moisture wicking t-shirt itself. 

It's a tricky question, however, as research seems to indicate that moisture wicking clothing has little if any effect on thermoregulation. Essentially what the science is saying is that currently researchers havent' found a significant difference in the body temperatures of athletes wearing cotton or moisture wicking t-shirts in hot weather conditions. The science is still new and hardly conclusive, but currently the claims by clothing manufacturers that their moisture wicking fabrics keep you cool haven't been substantiated by research. 

Compounding the issue is that since wearing layered, body covering clothing in the heat will raise your core temperature, it's important to regulate your body's heat. Overheating can cause a heat stroke which will kill you if you're alone in a survival situation. If you have to strain yourself, it's best to let some of that heat escape, and cover up during the heat of the day when you can get into some shade. 

In a non-survival situation, where you have an adequate water supply, a moisture wicking undershirt is the way to go. You don't want to be drenched in sweat and if you have the water available go ahead and let it escape your body. It might not technically cool you any faster but it'll make you feel a whole lot better. 

In a survival situation, the general rule is you want to keep your sweat on your body until you find an adequate source of water. Cotton may be the best material for this, as it absorbs water rather than wicking it. I honestly don't know what the answer is. 

Either way it seems you'll be fine, so long as you keep with the general rule of rolling up your long sleeves so you trap the moisture in. Even if the sweat is wicked from your skin, so long as it can't escape your outer shirt that moisture will find its way back to your skin somehow. At least that's what the US Army seems to say...

Slate has a good article about this, which you can read here.