(To the OP): Poly/cotton/wool etc - When choosing a good base layer to wear in winter, you have to consider how much you sweat. And how much you will need to stop. Wet=cold=dangerous if it's cold out, so you need to keep as dry as possible. You can generate a lot of heat moving, but it disappears fast once you stop. The difference between your own heat output and the ambient temperature becomes very noticeable in winter.
If you ride slowly, keep moving and don't sweat, you can wear anything, even cotton. If you go all out and ride hard, you will sweat, and then you'd better be wearing a base layer that wicks well, and not stop more than a minute here or there. Most of us will be somewhere in between, and our suggestions will be based on what keeps us reasonably dry and comfortable.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett