This is our most heavy-duty outdoor sock. When you're going to extremes like mountaineering, ice climbing and long backpacking treks, you'll thank SmartWool that you wrapped your feet in these. Heavyweight cushioning throughout the sock provides extra comfort, insulation and protection for extreme conditions. Elasticized ankle brace holds heel in place and allows for less bulk and greater forward flex in the boot. High Density Footbed (HDF) for improved performance, comfort and durability. Midcalf height is 2 inches taller than Trekking Heavy Crew or Hiking Medium Crew socks. QCActive.com (Active Endeavors) is your online source for Smartwool and Smartwool Hiking Socks. Smartwool Mountaineering Heavy Mid-Calf This is our most heavy duty outdoor sock When you re going to extremes like mountaineering ice climbing and long backpacking treks you ll thank SmartWool that you wrapped your feet in these Heavyweight cushioning throughout the sock provides extra comfort insulation and protection for extreme conditions Elasticized ankle brace holds heel in place and allows for less bulk and greater forward flex in the boot High Density Footbed HDF for improved performance comfort and durability Midcalf height is 2 inches taller than Trekking Heavy Crew or Hiking Medium Crew socks Smartwool,Smartwool Hiking Socks,QCActive,Active Endeavors