Smartwool Performance Mountaineering Extra Heavy Crew Extra-heavy full-cushioning keeps your feet warm and dry when you're mountaineering, ice climbing and multi-day backpacking. Arch brace holds the sock in place and adds additional support. Flat-knit toe seam keeps you comfortable. Contents: Made in USA of Imported Yarn: 74% Merino Wool, 25% Nylon, 1% Elastane.