Down insulation is incredibly warm for its weight — nothing else matches it gram-for-gram. If you're riding in bitterly cold, dry conditions (think interior British Columbia or high-elevation backcountry), down gloves or mittens will keep your hands toasty with less bulk than synthetic alternatives. They're ideal for low-output days when you're sitting on cold chairlifts or standing around at the summit.
The big catch: down loses almost all its insulating power when it gets wet. If you ski in coastal or humid climates where precipitation is common, or if your hands tend to run sweaty, down is a risky choice. A damp down glove basically stops working. Synthetic insulation like PrimaLoft or Thinsulate stays warm even when wet and dries much faster.
So reach for down when you're facing dry, extreme cold and can keep your gloves dry. For most resort skiers in variable conditions, synthetic is the safer bet.