I'll second that. Cotton is the most breathable outer shell windbreaker. Cotton should *only be used as a outer layer because it does not insulate. It stops the wind, holds in the warmth and lets out the moisture. The moisture freezes on the outer surface of the shell, and because of all your movement in biking, simply flakes off as it forms so it stays dry. Just shake it off once you come inside. I don't even pull out my cotton anorak until its around 0 deg outside because with my wool midlayer I'll be too warm. I paid $15 for it on eBay and when I wear it out it will biodegrade.
Beke- thanks for the suggestion for my next winter pants. My Ibex climawool (as an outerlayer to jeans) are only good to about 0 deg. Any good links for specific products online? I'm interested in the Mukluks, but I need them to have a sole...