Long before performance apparel replaced cotton T-shirts, the concept was in play: Think of men dressed in flowing white fabric riding across deserts on camels, or of elite runners cutting excess fabric out of their singlets. And ever since those sweat-soaked tanks were ditched for sweat-wicking fabric, apparel companies have been looking for the next innovation in keeping runners cool and dry.
"We're used to seeing a lot of technology in running shoes; now it's taking over in apparel, as people look for new materials -- everything from coconut shells to coffee grounds to various polymers -- to make a thin material that really moves a lot of sweat and gives the sensation of being cool," said Jeff Dengate, shoes and gear editor at Runner's World magazine.
Some of the newest technologies include fabric treated with Xylitol to react to sweat; New Balance claims it can lower body temperature by two degrees. Others use volcanic material to promote faster drying.
Despite such claims, however, the jury's still out on how well they actually work.
That's in large part due to the lack of human studies, said Michael Bergeron, a professor of pediatrics at Sanford School of Medicine of the University of South Dakota.
"The absolute key thing for sweating to be effective is you need to evaporate the sweat," he said. "If it's collecting in your clothing or dropping and hitting the ground, there's no transfer of energy."
Bergeron explained that clothing manufacturers try to change the microenvironment of air between an athlete's skin and their clothing. By wicking water away from the skin, it reduces humidity, promotes evaporation and helps cool the skin.
But, he added, "If it's hot and humid and you're working hard enough, you can still get into trouble."
Testers for Runner's World noticed that the fabrics with cooling polymers produced a subtly different sensation, although they were hard-pressed to pinpoint exactly what it was, Dengate said.
The perks may come into play most effectively under very specific conditions. If you can stay a little cooler in a 10-mile tempo run and hit your times while expending less energy, you could benefit from less time needed to recover, Dengate said.
"The hunt for innovation is always going to happen," Dengate said. "The question is, how much do runners embrace it? It can get expensive really fast. Shirts can cost $50-70. In all but the nastiest weather, [other shirts] work just fine."
Other cooling strategies are more important than the perfect outfit, experts agree. Acclimitization and hydration top the list, said Mike Sawka, who researched heat stress physiology at the U.S. Army Research Institute of Environmental Medicine and now teaches at Georgia Tech.
Allow a couple of weeks to acclimate completely, and keep in mind that you're unlikely to perform as well in hot, muggy conditions as you do in ideal temps. If the forecast calls for a heat wave, don a sweatshirt for a couple of workouts leading up to then, Sawka suggests. And hydrate appropriately: If you're sweating a lot, drink. If you're not sweating at all, your body doesn't need extra liquid.