Having bought some decent winter shoes I've been giving some thought to the best sort of socks to wear, and the number of pairs. My original sock philosophy with my ventilated "summer" shoes was to wear two pairs of cheap woolen or synthetic themal socks, which meant that my feet were packed into tight shoes and as a result ended up numb, even with overshoes on (although the overshoes helped with the cold). I put this down to poor blood circulation, but having read a few articles another factor might be the lack of air within the sock itself and between socks, feet and shoes. So wearing too many thick socks may just result in squeezing the air out or the socks and space around them. The thermal properties of wool, particularly from the merino sheep breed, are partly due to the amount of air trapped in the material, and silk then wool socks are considered a good combination.
I bought a £10 pair of Endura Baabaa Merino Winter socks, pictured, earlier this week and have found that wearing them with a thin silk sock underneath and my new shoes on top works well, with the shoes not too tight. I've only had 2 x 16 mile commutes this week to test them on though with temps just above freezing. Interestingly I found that wearing the Endura socks on their own and leaving plenty wriggle room for ones toes, worked the best, and having shoes tighter around the ankes to trap air in. So less may be more! Flexing toes regularly whilst cycling felt good and warm, compared with the numb feeling of cold lumps of meat I used to get using my old technique. Adding overshoes in really cold weather no doubt will provide extra warmth and rain protection.
There's quite a good article on keeping feet warm and types of socks on Page 50 of the Feb 1977 Backpacker - which is probably still relevant today Backpacker Page 50