Having completed two
Camino Frances from St. Jean to Santiago, during late April and May, last year and this, I recommend the following for socks, at anytime of the year:
1. Wear two pair of socks in your hiking shoes / boots (you should have footwear at least one and one-half sizes larger than your streets size to accommodate this.) The inner pair of socks is a synthetic or silk liner, intended to wick moisture away from your feet. The outer pair should be merino wool and thick. They function to cushion your feet, absorbing pressure, reducing friction from your hiking shoes / boots, and allowing moisture to evaporate. NEVER - EVER - used cotton socks - PERIOD.
2. Carry two "sets" of the above socks. This totals four socks (2 liners and 2 outers).
3. Wear one pair of the above. So, your total need is for three "sets." This is a total of six socks (3 liners and three outers).
4. The inner socks can be worn as casual socks with your apres hiking footwear. I also sleep in the fresh pair of liner socks I will wear the following day as I must cream / moisturize my feet nightly with a special moisturizer to reduce calluses.
5. Based on experience, I recommend liner socks in a dark color like navy blue, black, or brown as they do get crummy looking after a few weeks. On my first Camino I wore white Cool Max socks. By week two, I wanted to toss them, but they remained functional. So I kept them until the end. But, I ended up buying brown casual socks along the way to wear in the evening with sandals solely for appearances sake. This year, I used navy blue Cool Max liner socks. They were likely as grundgy looking, but the ground-in and set stains do not show.
5. If you encounter unseasonably cold or wet and raw weather, a pair of outer wool socks can also serve as an expedient pair of mittens. This is a basic winter survival skill that I recommended to many pilgrims along the way, both last year and this.
The "three-pair sock system" permits you to have one pair on, one pair dry and ready to go for the next day, and the third pair; having just been washed, either dry, or drying. You can always use a safety pin to attach these four socks to your rucksack to finish drying if the day is not rainy.
I have observed that some people try to save a few grams by obtaining socks that supposedly combine the wicking aspects of the liner socks AND the cushioning aspects of the outer, wool socks. I believe this is false economy, as the separate socks have utility beyond simply wearing them with hiking boots. I have described this above.
However, I have also used a liner sock that I was hand washing in the shower as a wash cloth as well. Typically, a synthetic liner sock is soft, like microfiber. A unified pair of socks that seeks to do it all would be scratchy, and likely do neither wicking nor cushioning as well as the layered system, at least in my experience.
BTW - in my two complete
Camino Frances, and using this system, I have not had a single blister on my feet. I am fully aware that everyone's feet are different and no two people will have the same experience. So everything I have stated here is offered with that caveat. However, this year, I did get one blister on my right thumb from my walking sticks. But that is another story...
I hope this helps someone.