This is one of those items of which you feel like buying another, just in case Castelli stops making it. It is light but breathable, thin but as others have said, not really packable. It keeps me warm on rides in the New England low 30's, overcast and slightly windy with just a thermal long-sleeved jersey underneath it. It stays pretty well put whether in or out of the saddle. The material is soft to the touch, but not floppy and doesn't rustle with wind or movement. The zipper has a long pull tab and slides up and down very easily, so it's not a chore to zip or un-zip for ventilation as needed. Construction quality is terrific. For reference, I'm 5 foot 8 inches with a 39-inch chest. I bought the large which is perfect for one or two layers underneath. The only thing I would add if I could, would be under arm vents. Those work great for me.
This review is after a few rides on gravel with temps in the upper 30s. It is not a thick jacket so it is warmer than I expected with just a long sleeve jersey under it. It totally blocks wind. When climbing for several miles on a sandy road, I did get a bit hot. This should not be a problem for less strenuous riding. It does roll down just barely small enough to put in a jersey pocket, with some sticking out the top. When putting it back on for descents though, it gives fabulous relief from the cold wind. I could use some tights/pants with this material on the front. The xxl fits well over an xl long sleeve jersey. I think adding zipper vents would make it near perfect.
This Castelli Men's Go Jacket is a go-to item on a cold autumn or winter day. It's thicker than your average wind stopper and keeps you dry on light rainy days, yet still manages to breathe well so you don't overheat. It's not really a packable jacket (it doesn't really get compact enough to fit in a back pocket or small handlebar bag), but I tend to just unzip it when the weather warms up (or on strenuous climbs) which is enough to keep me from overheating. I appreciate the pockets in the back since many other jackets require that you reach under them to get to your jersey pockets, making it easier to grab a gel, bar or phone. It's got some good reflective accents to keep you visible in low light, just remember to size up since Castelli tend to measure using svelte Italians as their standard. Overall, this is a very solid and dependable jacket.
Super light, wind/water proof and fairly warm for a thin jacket. I have done rides in the 30's w/just a Castelli Base layer and remained warm and dry. Nice discount from Bikes direct so overall very pleased! Fit was snug but not Euro Cut. Very pleased overall.