The 40 Below K2 Superlight is the choice for Alaskan and Himalayan climbs! An excellent overboot to use in conjunction with "step-in", "new-matic", "strap-on" crampon bindings and "wire-bail style" ski mountaineering bindings. Patterned to fit both plastic and leather mountaneering boots. This model incorporates a special nylon covered, 4.7mm neoprene stretchy closed cell foam insulation, with two layers of heat reflecting titanium, that goes completely around and under the boot with no gaps in the insulation. They fit trim to the boot and are not bulky. Because of their stretchy nature they are easy to put on in the cold, they roll up small in your pack and are easy to repair! The upper gaiter area is made of windproof and breathable Cordura nylon to minimize frost build up. The toe and heel area have a small triangular shaped area of thinner insulation that allows for many bails of "step in" and "strap toe/flip lever heel" crampon bindings to compress the insulation and rest on the toe and heel groove of the boot. The toe, heel and lower side area of the overboots have a rubber paint applied to add abrasion resistance and help to protect the stitching. A full length 2" wide heavy duty Velcro front closure with elastic drawcord & cordlock top closure, allows for easy adjustment of boot laces or buckles, all the way to your toes. A special nylon crampon patch is glued and stitched to the instep side of the neoprene for added resistance to crampon pokes etc.