In reply to Stani49: I used to use the Smartwool Mountaineering socks but now use Icebreaker Mountaineer Socks when really really cold, they are a bit thicker and a bit warmer than the Smartwool ones. But the difference between a new pair and one that has been used / washed a few times is even greater. More important is the boots, having sufficient wriggle room for your toes, keeping the inners warm etc.