Jonno, you must have some great headgear if you walk around in just a windproof and a baselayer in winter. The Marmot DW is light but does have insulation.

Ben I've worn just a Marmot baselayer and a Fuera Smock at temperatures around about zero degrees probably down to -4 if you factor in the windchill. As long as I kept moving I was o.k. not comfy but o.k. The only headgear I had on was a buff and I was wearing gloves.