New and improved with a 4 degree Elite Fit System and ReliaWool high density impact zones, SmartWool PhD Outdoor Heavy Crew Socks deliver more comfort with an improved fit and greater durability. . 4 Degree Elite Fit System improves fit and comfort four elastic bands gently wrap and support the foot and allow for greater stretch and recovery while the foot flexes. Four elastic bands: ankle band, upper and lower instep bands, and arch band keep the sock in place. ReliaWool high density impact zones provides longer lasting protection to keep feet comfortable. Strategically placed mesh ventilation zones provide ventilation for temperature and moisture management. Soft merino wool regulates temperature to keep feet warm when its cold and cool when its warm, manages moisture for breathability, naturally resists odor, and does not shrink or itch. Heavy full cushion for maximum impact absorption and insulation. Flat knit durable toe seam for high burst strength. 1x1 ribbed welt. Overall height: 8.5 in.. Machine wash and dry inside out.