Anyone else notice that federer is wearing what looks like a black (cotton?) Vneck shirt under neath his dri fit polo shirts? I will try to find a picture. I am wondering what are the benefits of wearing the extra shirt? I am guessing it might be more comfortable, warmer if it is chilly or windy outside since its easy to get cold while wearing dri fit or maybe some other reasons. As far as disadvantages, you get a little less mobility both from restricting movement and more weight. With how much federer helps Nikes revenue, I don't think it would be a problem for Nike to create federer a shirt of what ever material/ specification he would like.