Darn Tough polyester Performance Fit: No slipping, no bunching, and no blisters. True Seamless: Undetectable seam fusion for an ultrasmooth, invisible feel. Fine Gauge Knitting: Unprecedented durability and our unique "put it on, forget it's on" feel. Fast Action Wicking: Pulls moisture away from skin. Fast drying; Naturally Antimicrobial: Repels bacteria and odor. Merino Wool: The ultimate fiber for breathability and comfort in all conditions. Still made in Vermont, USA. Still unconditionally guaranteed for life.