Merino Wool is nature's original technical fiber with proven performance qualities. It is a true 4-season fiber with the extraordinary ability to provide warmth in the winter and cooling in the summer. The unique structure of Merino Wool fibers absorbs moisture without feeling soggy or losing the ability to regulate temperature. Swiftwick PURSUIT™ is engineered with fine-gauge Merino Wool which produces a soft, no-itch feel from cuff to toe. Merino Wool is a naturally renewable resource and is sustainably sourced. Swiftwick PURSUIT™ and PURSUIT™ HIKE are collectively available in 8 different cuff heights.