Polyester is the material.
>>Mostly technical variations of polyester. Every major athletic brand uses them. They dry faster than cotton so you stay drier and don't have the material chafe your skin like cotton.
The yarns they use to make the material are smaller than cheap polyester, so they wick moisture from your skin and dry quickly.
Whatever brand you choose, make sure you look for flat-seam construction too, to reduce chafing even more.
Under Armour makes cool stuff but look at small brands like Hind, Brooks, Asics, Sugoi too. Smaller brands usually make a higher quality product.<<