What Our Gearhead® Experts Are Saying:"I wore these on a winter hike that turned icy near the ridge, and the ICETREK outsole held on sections where I would normally slow way down. My feet stayed warm the entire time despite temperatures that dropped well below freezing."Winter terrain rewrites the rules for footing, and the Mammut Aenergy Mtn Mid Winter GTX Boot is built with that shift in mind. Head out on a frozen trail where packed snow gives way to glazed ice near the ridgeline, and the Vibram ICETREK outsole holds its grip through the kind of surfaces that turn a confident stride into a cautious shuffle in lesser boots. GORE-TEX Duratherm insulation keeps 220 grams of warmth locked in without adding bulk, so feet stay warm through long stretches in freezing conditions. The Mammut Basefit System and 3D Heel Foam work together to lock the foot in place for stability over long miles, while a zip-up gaiter over the ripstop upper shields against wind driven snow before it ever reaches the lacing underneath.