His ideas obviously work in the worst possible conditions and deserve our attention. He has plunged into freezing water, then spent the night in sub-zero weather without drying off, or having the benefit of fire or shelter, to prove the effectiveness of his clothing ideas. They would be an excellent investment which I recommend. Drinking plenty of water is vital in cold weather. You dehydrate faster in cold weather than in hot weather.
Dehydration is a precursor to hypothermia.
Wool, while better than cotton, is still not good for extreme cold conditions because it retains water. His special clothes, boots, and sleeping bags, are based on using open cell urethane foam. Trapped air is what really insulates, and the thicker the material trapping the air the more insulation it will provide. The most dangerous winter clothing is cotton long underwear because it can kill you in cold weather. Don't waste money on Goretex or other similar materials.