Reviewed by Ludwig - 4th Oct, 2018 painful I have been using the blue insoles for a while for shorter walks of about 3 hours duration and in this time I had no problems with it. Last week I started a section of a long distance trail and after about 8 miles I felt a distinct discomfort in the inside of my left heel. When I had a closer look I could see that the grey hard plastic was digging into the side of my heel. I tried to cushion it with paper, but by the end of the day it was very painful to walk and a similar pain had started on the right heel. The grey plastic support is very sharp and though cushioned by the foam above, it forms a ridge distinct enough to creat a long blister.