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We sent our merino/synthetic Fast Mountains to an independent tester who compared them to two leading brands' merino wool hiking socks. In the abrasion test, the other socks averaged 1,800 rubs on the machine before wearing through. The Fast Mountains achieved 10,000 rubs before the testers finally shut the machine off, admitting that these socks weren't about to wear out. In the tests, our socks also dried and wicked faster than the competition. 33% merino wool, 33% polypropylene, 32% nylon, 2% spandex. Merino wool and synthetics integrated into one yarn for superior durability. Fast wicking, fast drying. Abrasion resistant, antiblister, super soft. Spandex arch band offers "memory fit". Breathable mesh-knit instep panels. Cushioned sole and instep. Reinforced heel and toe. Made in the U.S.A. Medium fits women's shoes size 4 to 7.5. Large fits women's shoe sizes 8 to 11.