The Darn Tough Spur Boot Sock Fatigue is a light weight unique sock that offers a performance fit that integrates perfectly with your boots for miles of comfort. The men's 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 boot height sock is light and strong with a versatile construction. It comprises of 50% nylon, 45% merino wool and 5% lycra?Â« spandex.