I read all the above posts with great interest. Last year I walked the
Camino Frances and had no blisters at all. I attribute this to wise advice at my local REI shop where I was fitted for my Keen Targhee II mid-height hiking boots by a fellow who was an experienced thru-hiker. The combination of oversized hiking boots, two pair of socks and proper foot hygiene did the trick, IMHO.
On the other hand, my life-long struggle with heel calluses almost ended my Camino early. While I trained for my Camino at home, I wore green Superfeet insoles with my boots. The different Superfeet models and stiffnesses are indicated by the insoles color. It turns out that the relatively rigid molded plastic heel cup on this (green) insole rubs against my heels and causes the calluses to grown. I eventually found proper medical attention from a podiatrist at Burgos.
This experience taught my several things with regard to insoles:
1. If you prefer after-market insoles to what came with your shoes or boots, make sure the heel cup does not rub your foot as it rides up and down in your shoe - boot. There are other Superfeet insoles (orange, or berry colored) that are designed differently and while they have good support, do not have the same rigid heel cup as the green model. Check the stiffness of the heel "cup" out before you buy something.
2. If you have odd feet, or foot issues that make you different than the mass of people, do see a podiatrist BEFORE you depart. As I prepare to walk the same Camino again this year (to ensure that I walk EVERY kilometer that I skipped last year due to the foot issue), I placed seeing my local podiatrist high on the pre-Camino "to-do" list. That was done in early February. The podiatrist recommended a foot ointment that uses enzyme action to remove calluses and soften feet. It actually seems to be working. The product is named "Callex" and is available commercially or online here in the U.S.
3. My podiatrist also made custom orthotics that fit in my huge - size 47 / US 13 - hiking boots. Having worn orthotics before in street shoes (sized 45/11), I knew to specifically ask for the sports-style orthotic that can be immersed in water without damage. The new insoles are what a runner would use. Hence, while my "street" orthotics are fabricated from leather, felt, and cork; my Camino insoles are totally synthetic. Given my experience slogging through mud and paths that become streams in the rain, I think this was wise. They were not cheap, but certainly cost less than an interrupted trip.
3. I know there is a slight weight penalty, but I plan to carry my original Keen insoles with me at the bottom of my pack. This is so I can either give my prescription orthotics a rest occasionally, or switch them out if the prescription insoles do not dry completely for the next day.
No matter what kind of feet you have you must have at least the insoles that came with your shoes or boots. The "naked" boot usually does not provide enough padding or shielding against the stones you walk over every day on the Camino. I experienced this last year. I had to walk a day without an insole and felt literally EVERY stone and pebble. It was not fun.
I hope I have added value and this, all together, helps someone.