Soldiers encounter all sorts of weather conditions on the battlefield: blistering winds, broiling heat, drenching rain. Through it all, they face one constant problem: What to wear? Soon, their fashion dilemma could get a little easier.

According to a recent call for research proposals, the Army is on the lookout for a fabric that could adapt to temperature. This "environmentally responsive" material would keep a soldier not too hot and not too cold, constantly adjusting to outside conditions as well as body heat. Think of Marty's super self-drying jacket in Back to the Future II – only in camouflage.

Right now, soldiers tote around multiple layers that offer different levels of cold and wet weather protection. While versatile, all those clothes are still pretty heavy and take up a lot of space. Combining many layers into one would mean less weight and more freedom to move. But it's a tricky feat to pull off: not enough warmth could mean hypothermia or frostbite. Not enough cooling power could mean heatstroke or dehydration.

So how exactly would the Goldilocks fabric work? According to a paper referenced in the Army announcement (.pdf), one possible mechanism would be to use the principle of a "bimetallic thermostat." Basically, you use fibers that contain two metals bonded together in a tiny spring. As the temperature drops, one metal changes its length more than the other one — resulting in a "curl" in the fiber. If you have a whole shirt made of this stuff, it would actually change thickness as it got colder, providing more insulation and warmth.

Whatever method is used, the Army's got a specific idea of what they want the smart shirt to do. First, it's got to measurably increase "clo" values in colder temperatures. One clo is the difference between being naked and wearing a typical business suit; who knew there was an actual quantifier for that? Second, it's got to be army-laundry tough, withstanding at least 20 washes. And finally, it must be hypoallergenic and "inert in nature" – yes, I too would be wary of chemically unstable Under Armour. The first model doesn't have to be flame-resistant; that's an extra feature that will come later.

But soldiers in training or combat aren't the only ones who could put a smart shirt to good use. The Army imagines all sorts of other applications in civilian markets, such as outdoor recreation or law enforcement. Eventually, this magic fabric might even make its way to your local Macy's – which would be pretty cool. Literally.

Photo: DVIDSHUB

See Also: - Special Forces Getting High-Tech Soldier Suits for Iraq Mission