The temperature here in Boise has been around zero degrees F for the past week, and I have been riding my Catrike Speed to work everyday. The combination of clothes I have keeps me warm all the way, and my only problem is my glasses and ski goggles fogging up sometimes. My clothes are an example of the layering system. The first layer is thick wool blend socks, polypro long underwear top and bottom, and thin polypro liner gloves, as shown below.
The next layer is an insulating layer, which is added to the base layer. This includes Keen cycling sandals, North Face cross country ski pants which are windproof, fleece gloves where are the inner part of a pair of winter mountaineering gloves (Chouinrd winter gloves), fleece neck gaitor, head covering by Pearl Azumi, and Expedition weight Patagonia Capilene pullover. I have a down coat I could wear, but at around zero degrees it is just not needed.
The outer layer is made up of Marmot uninsulated goretex wind pants which zip all the way up the leg, Sidetrak neoprene boot covers which leave the cleat on the bottom of the shoes exposed, the nylon outer gloves of the Chouinard winter gloves, an REI goretex raincoat, a cycling helmet, and a waterproof helmet cover. Not shown are my ski goggles, which I wear over my glasses unless they fog up.