Mammut Alpine Winter

This mummy is stuffed with 850+ fill down and protected by Sea to Summit’s 3D NanoShell.

Brand: Mammut

Model: Alpine Winter

Love down, but fear packing it into soaking conditions? Get the Alpine ApII. This mummy is stuffed with 850+ fill down and protected by Sea to Summit’s 3D NanoShell. The DWR-treated nylon shell is lined with a thin “3D Barrier” of continuous-filament synthetic insulation that allows sweat vapor to exit—without condensing on the inside of the shell and wetting the down. That’s critical on longer trips, when moisture accumulates and doesn’t have time to dry. “It maintained its loft through five humid nights, even when tent condensation dripped down on the bag,” reports our tester after a climb on Washington’s Mt. Baker, where the bag kept him warm to its 5°F rating.

The offset baffles lock heat in, as does the smaller-than-average face opening on the hood. The narrow footbox heats up fast, so that even when chilled to the bone from a wet slog to basecamp, our tester felt head-to-toe warmth within 15 minutes. The 60/40 down distribution places more insulation on top, which side-sleepers sometimes find chilly, but our tester felt no cold spots even when tossing and turning.

Fit is trim: Our 5’6” tester calls it “perfect,” but bigger campers found it cramped.

Tradeoff: The 3D barrier makes it bulkier than most down bags (compressed, it’s the size of a toaster oven).


3 lbs.; 5°F; reg. and long
Extremely lightweight materials and the newly developed MTI 14 insulation make the Alpine bag one of the lightest synthetic sleeping bags around. Light TX shell fabric is featherlight, windproof and highly water resistant.

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