The Free X9 sock is based on the standard Free 9 sock design, except it has slightly more elastic woven in and a taller elastic band on top of the cuff. The idea is for some additional support over the standard version.
The entire sock body is constructed of Meryl Skinlife fabrics which does a great job at wicking moisture away from your foot while providing plenty of breathability and air flow. The top of the instep has a diaphanous web knit, meaning it is thin, light and airy, while the rest of the sock has a slightly thicker blend for a bit more support. Choose size and color.