Back in the 1870's when I used to backpack a lot, 2 pair were worn to help reduce blisters and provide some more cushioning. The inner pair was supposed to be a thin sock. I never liked the feeling. It felt I was sliding around in my boots. Eventually, you could buy socks that were designed to reduce blisters by having 2 socks made into one unit but I never tried them. They seemed to be mostly designed for runners and I could not find them in styles high enough to wear with boots.

This article seems to be pretty good. The gist I got out of it after a quick skim was wear 2 acrylic socks -- one with good cushioning. But clearly in some situations, you are just going to get blisters.

The other day, I was watching some show called "Survival School" on the MOJO channel (I am not making this up). The show followed a bunch of students through the U.S. Air Forces' S.E.R.E school. During one segment the students had to hike many miles across mountainous terrain with heavy packs. Some of their feet took gruesome beatings. One student lost the entire bottom callus of a heal.