Many are missing a huge factor for hunters getting cold feet and in fact it's a simple law of physics. Metal and even wood actually draw heat out/away from boots. They literally suck the heat out of the soles of your boots, regardless of what kind of material and the boots and insoles are. That's why it's actually easier to keep your feet warmer on ice/frozen ground than it is when off the ground on a metal or wood platform stand. (This is also why the various "boot blankets" help as well as they put a layer between the boots soles and the stand platform.)

Thus the first GREAT aid in fighting the "icy feet" is a simple piece of heavy carpet, or foam or even the likes of a simple carpeted door mat carried with you and placed between your feet and the platform of the stand. As for boots, Sorel packboots and other wool/poly inner-boots and insoles are CONSIDERABLY warmer than even the warmest, heaviest insulated rubber knee boots. The A #1 most critical factor in insulation is moisture management which means getting rid of that moisture. (Thus the principal of both heat and A/C in any mechanical device like a refrigerator or HVAC unit) Boots and indeed all types and layers of clothes call for the same need, evacuation of moisture. Knee boots are THE WORST for such because they are so encapsulated, in essence your feet and legs are "rubber dipped".