The right gear can make or break any expedition. That's why we've created the new PhD® Outdoor Mountaineer socks, our most technical mountaineering socks ever. We put some serious sock science to work in these all-mountain socks, including revolutionary Indestructawool™ technology for ultimate durability and the 4 Degree® elite fit system for a dialed fit. We placed high-density cushioning where you need it most, in the heel and toe, while using a flat knit on the leg to accommodate low-volume mountaineering boots. Mesh zones offer breathability, flex zones offer added comfort, and Merino helps keep feet warm, dry and comfortable.