The PhD Ski Medium has an improved 4-Degree Fit System, new reinforced smartyarn, and full, medium weight cushioning for maximum warmth, fit and durability.
Just purchased these, but have not yet gone on the slopes yet to use them. I wore them around the house and around town in California. They are very comfortable and fit on my walking shoes nicely. Keeps the feet toasty, but always dry. (I have very sweaty palms and feet) Very comfortable. I highly recommend.