Alex Fleming wrote a review of CamelBak Racebak Hydration Men's Jersey on March 23, 2011
I've taken this jersey on multiple 50+ mile endurance rides and two hour road bike races in Texas. Neither did I over heat or feel constricted in my movements. I have a 40" chest and the medium fits loosely enough to breath normally but snug enough that the bladder does not slide around on my back. A normal cycling jersey/shirt over this racebak does help as well to keep the racebak in place.