The best hiking and trekking outdoor sock SmartWool has made to date. Ideal for aggressive, multi-day treks with heavy backpacks. Their medium full-cushioned PhD Outdoor Medium Crew is their most versatile outdoor sock. Thanks to WOW technology in high density impact zones, shock and abrasion are reduced. The 4-Degree Fit System keeps the sock in place. Made in the USA of New Zealand Zque Merino wool.