The Darn Tough Micro Crew Ultra Light Cushion Merino sock lets you lose without giving up the comfort. The sock features merino wool, fine gauge knitting, fast action wicking and true SeamlessT to offer an ultra smooth, invisible feel. The sock is guaranteed for life and is naturally antimicrobial. The micro crew height sock is ultra-light and ultra-comfortable. It comprises of 51% merino wool, 43% nylon and 6% lycra?Â« spandex.