I came upon some more winter riding blog fodder on my Sunday insta-freeze ride when both Eric and I decided it would be a good idea to get one foot wet. Normally this would be less than uninteresting, except that after about five minutes my wet foot was much warmer than my dry one whereas Eric's wet foot was uncomfortably cold compared to his dry foot. The most likely explanation for this was our respective choices of bootie:
Both booties are pretty iced up, even before we went and dunked ourselves in a river, but while my bootie provides a nice tight seal all the way around (it has a full rubber sole), Eric's is pretty tattered and loose. When my foot got wet, the water formed an even thicker crust of ice over the bootie, sealing all the seams and preventing any airflow in or out. Eric's, well, didn't so much. My hypothesis is that the sealed bootie became a vapor barrier, locking in moisture and thus saving heat. Eric's booties retained some heat, but were ventilated enough that evaporative cooling could make his foot really cold. The conclusion, maybe vapor barrier liners are a worthwhile investment for cold weather riding. At $8 for socks and $15 for gloves, it's certainly worth a try. I'll order some and let you know.
You should also check out the entire Warmlite catalog (the people who make the vapor barriers). They make great camping stuff and the catalog is delighfully vintage, but OMG SO NOT WORK SAFE.