Nikwax Basefresh is supposed to revitalize tech (synthetic) athletic clothing in a way that is supposed to refresh its wicking properties and keep it from smelling longer. You use it in conjunction with your usual detergent. I also used it with the Nikewax Basewash, a synthetic clothing cleaner.
It took me awhile to tell whether this was actually effective or not, but I think it did. Using it in conjunction with the Nikwax Basewash, it overall seems that it again takes longer for my tech running clothes to start to smell bad.
Overall I find it difficult to judge whether they wick any better or keep me any warmer/cooler, but they definitely hold of my runner-stink better than they were.