I've done some rides in this jacket with air temps of 30-40 degrees with one to two layers underneath and I stay snuggly warm. It's magical how it wicks sweat but still feels breathable compared to other wind proof jackets I've worn. When I first put it on, I was unsure about the cut, but then I bent over into bike position and it's cut perfectly! I wear an XS is almost everything but in Castelli I tend to size up, especially if layering. I went with Small and it's just right. The tall collar is awesome. Never dreamt I would spend this kind of $$ on a cycling jacket, sure glad I did. Love.