Originally Posted by Carbonfiberboy

I'm also confused by this entire thread. I'm a roadie in the PNW who rides year-round but only when it's not icy. I use 3 layers when just a summer jersey isn't enough: baselayer (Craft, SS or LS), and a jersey of the necessary weight for the conditions (2nd layer), and either a wind vest or wind jacket or neither, as conditions warrant (3rd layer). I dress so I'm shivering in the parking lot before the ride. That's perfect. The 3rd layer goes off and on as conditions change during the ride. I can put both my vest and jacket in my jersey pockets, meaning that my outer layer is light enough to stuff there. I can't think of a reason not to wear a bike jersey as 2nd or "mid-layer."

Below freezing is a completely different story. My mountaineering and Alaskan experience is that one should wear sufficiently warm clothing to be comfortable at rest and then attenuate effort to prevent sweat wetting out your clothing and thus ruining your clothing system. The vest on the outside of the wind jacket is a good way of doing this, as is a full down jacket or suit. Moisture transfer is the single most important key to staying warm while active. It was my Alaskan practice when resting to move on when my fingers and feet grew numb, taking up the activity level enough to re-warm them. That was never enough to induce sweating, but that's just me.

Using cycling jackets which combine windproof or water resistant and insulation has not been successful for me because of the moisture transfer issue.