I always use a liner even in the summer time. I usually use a very thin nylon liner under some sort of wool sock, again, whether it is in the winter or the summer, I use the same set-up. This helps keep my feet a little dryer and both the nylon liner and the wool sock will dry out pretty quickly whenever you stop for a rest on the trail. It also lets the nylon liner take a lot of the friction and wear and tear so that I have trouble with blisters much less than I normally would..sabre11004...