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.