For really tough hiking, like when I am elk hunting, it used to be a pair of synthetic socks beneath a pair of wool boot socks. I never like the feeling of pulling an extra pair of socks over my feet, but I like blisters even less. Then I found Thorlos, and I wear just the one pair now. They have a sock liner that you could use if you felt you really needed to, but since I went to Thorlos, I don't get hot spots, my feet feel drier, and they don't wear out as fast.