Mountaineering For the most warmth on very cold, high-altitude, or long trips, choose double boots, which have a weatherproof plastic or synthetic-fabric outer shell over an insulating inner bootie. Single-layer boots are more responsive and comfortable on lower, warmer trips. Also consider sole rigidity: You’ll need stiff soles for front-pointing up steep slopes with crampons–but they make for clunky walking. Choose lighter, more flexible soles if the focus of your trip is hiking, not climbing.
Skiing Low-cuff, two-buckle boots are best for flat touring; high-cuff, four-buckle models give maximum control on descents. Mid-cuff, three-buckle boots are a popular compromise: comfortable enough for skinning up, stable enough for skiing down. If you’ll be camping, remember that the liners in double boots will dry faster than insulated single boots in a tent.