I bought this jersey for the occasional time trial and as an option for daily hot weather rides. First of all, Castelli medium jerseys of all types fit me perfectly. Not loose and not tight. This one, on the other hand, is the smallest jersey I wear. It looked hilariously small when I took it out of the package. Unzipped, it hangs under my arms. Nevertheless, it stretches very easily and is very comfortable, except across the front of my collarbone, where there is an unusual amount of pressure whenever I'm upright. (36" chest, and not overly muscular shoulders, but not Schleck-like either). I think the low cut of the collar, the intended riding position and the snug, stretchy fit all contribute to this. Until I took off the little Castelli pull that was attached to the zipper, I could lower the zipper an inch, and then unzip it to my waist just by throwing my shoulders back. But I think that was caused by the pull preventing the zipper from laying down. The rear pockets are very functional, and hold things securely, but I'm paranoid about carrying phones or keys in them because of the side opening, but that's just me. Besides, the jersey isn't really intended for that. All in all, it's a very light, comfortable, skin-like fit, with just the right amount of room in the shoulders and arms, which come right to the elbow for some bonus sun protection on daily rides. Very thin, very stretchy and therefore, very revealing. Think thin skin. Some might be bothered by the aesthetic of the cut of the collar, which is similar to a performance t-shirt. Great jersey for the intended purpose. Fits as intended, but if you think your Castelli jerseys are too tight already, you may very well have a problem with this one, Very comfortable except beneath the tightish low-cut collar in front when not in riding position. It's my go to jersey for hot weather road rides.