Two stiffnesses of plastic are used to provide rigidity and flexibility for mountaineering and ice-climbing. The soft Pebax shell will not stiffen up in cold weather, and the inner liner features a warm, lace-up liner. Fully rigid boot with a hinged Pebax nylon shell that stays flexible in cold temps. Included liner is 4-6mm thick. Expedition liner (6-8mm) is available separately. Relatively high volume toe box. Shock-absorbing heel insert. Cork insole for added insulation. Removable footbed. Sole rocker allows for comfortable walking and it uses a durable Vibram rubber outsole.