Lesson learned the hard way...more material isn't always good. Make sure there is enough room in your shoe for extra layers of socks. If the shoe has them all compressed, the extra layers get compressed an the insulation value of them disappears. I learned this at the turnaround point of a ride in 15 degree weather, 15 miles from home. I did not get frost bite on my feet, but they were REALLY hurting by the time I got to a place to warm them up. Since then I've gotten smart-wool socks and wear 1 layer and have been fine for hours outside at 15 degrees and below.