Works like a good baselayer should
I purchased this three weeks ago just in time for nasty weather two consecutive weeks in a row. This works great under a thermal jacket or any jacket, and even under loosely fitted jerseys. It kept me warm on chilly days (40F to 55F) and wicks moisture like no other. As for the fit, I am 5'5", 160lbs with a 30" waist and a 38" chest, I got the small/medium size. Yes it is tight, but not uncomfortable, it's made to hug the body especially in the riding position. If it fits too loosley it will not provide you any warmth on those cold rides and its moisture wicking capability will go down.