Salewa Boxer Cristallo Warm Alpine Merino is the perfect base layer boxer for high-intensity mountain activities in colder temperatures. The hybrid merino wool and polyamide Alpine Merino Responsive base-layer fabric combines thermal efficiency with excellent moisture management. Its fibers are made of fine merino spun around a polyamide core for additional stretch and durability. The polyamide also contains thermos-reactive Responsive technology, which recycles natural far-infrared (FIR) energy to improve your thermoregulation for greater comfort. As Responsive is an integral part of the fabric yarn, it does not break down or wash out.