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. Swiftwick PURSUIT™ is engineered with fine-gauge Merino Wool which produces a soft, no-itch feel from cuff to toe. A favorite at Swiftwick HQ for cycling and trail running. The Four height sits below the calf and its double-cuff construction provides extra support for cycling and trail running.