100% waterproof and thermoregulating, the Bircham excels in high-intensity sports, as well as more relaxed outdoor pursuits. Handcrafted in the Sealskinz factory in Norfolk.TechnologyOuterExtra-durable polycolon and nylon blend, with 4-way stretch for an optimal fit.Mid-SectionAquasealzwaterproof membrane releases moisture vapour from inside the sock.InteriorPremium merino wool for comfort and sweat-wicking. Natural antimicrobial properties, inhibiting growth of odour-causing bacteria.The Bircham combines premium merino wool with performance-driven, engineered fibres. The outcome: a highly functional sock with a natural feel. Each stratum of the Three-Layer AquasealzComposition assists in the release of internally generated moisture, aiding thermoregulation. The Aquasealzhydrophilic membrane is completely waterproof, keeping feet dry in the wettest of conditions. Ankle length complements the overall breathability of the garment. Mountain biking, trekking, trail running a