Smart, intelligent, reactive and performance textiles are all the rage in design these days. A recent article in Businessweek Online says we may want to consider otherwise though.
As an avid cyclist and triathlete I have some experience with these materials, though not many of the higher end ones. I haven't update my wardrobe for quite some time actually. I've never owned any of Under Armor's apparel.
I am skeptic of the ability of the clothes to perform at various claimed levels. I imagine the difference between wearing jeans on a bike and spandex is easily recognizable to most people. If nothing else, I know I sweat less while wearing spandex when cycling than while wearing jeans. The difference between spandex and tech-x might not be so recognizable [ a fun little mathematical expression of that; jean:spandex > spandex:tech-x]. The added performance of tech-x is not in proportion to its increased expense. It really only matters to those athletes in the top 5% who are going to be setting world records in their disciplines. Everyone else should relax, eat fewer power bars, drink less gatorade and just have fun.