What material is used in under armor?
100% Polyester, or as some marketers call it: PolyArmour. Haha.
Underarmour developed a way to manufacture polyester so that the
body's moisture will be kind of sucked through channels of the
special polyester (synthetic) fabric instead of being trapped near
an athlete's body, such as cotton would do. UA calls it "moisture
wicking."
That answer comes from Wiki, so take that under consideration as
you go forth... and sweat!