I have been using these socks for a few weeks now. Normally I run approximately 10-15 miles per week. One of my runs is usually over five miles in distance. I always had the problems of blisters on my heel using normal cotton socks. Since using these socks, I have not experienced any blisters on my heels. I ran 7 miles this past Sunday and not one blister. I will be running 8 miles tomorrow, and I am certain I will be blister free.