The challenge: Keep down dry without inhibiting breathability, which it needs to reach maximum loft. The solution: Sea To Summit’s 3D NanoShell. The shell itself is fairly standard: 20-denier ripstop nylon with DWR. But hidden just underneath that shell is a thin layer of continuous-filament synthetic insulation. This innovative feature allows sweat vapor from within the bag to pass through, but it traps condensation going the other way. The idea: By preventing moisture from migrating into the 850-plus-fill down, down stays lofty over the long term.
Does it work? “The Traverse puffs up like it’s stuffed with helium,” says one tester, “and it maintained that loft during a week of subfreezing nights in Capitol Reef National Park.” Other well-conceived details: The zipper guard is made of exceptionally light and stiff 210-denier poly cloth used in racing sails; it never snagged once. The precisely shaped footbox—tapered in three directions—is among the best we’ve tried. “Volume wise, it’s a fairly small chamber, so it’s easy to heat up, but the perfect anatomical shape mirrors the natural position of my feet so I never felt stifled or restricted,” says one tester. The hood is roomy yet contoured, with drawcords that are built deep inside the hood baffles and away from the face. Down is divided 60/40 between the top and bottom.
The mix is great for back- and stomach-sleepers (at least those who roll over inside—not with—the bag). “The Traverse is as warm as it claims to be,” says one tester who used it on a weeklong November trip in Utah—but side-sleepers reported chilled backs. A full-length, two-way zipper, combined with a foot vent, lets you micromanage ventilation in milder temps. Bonus: A silnylon compression sack is included. Bummer: For the price, we wish it was a few ounces lighter and more compressible. $500; 2 lbs. 6 oz.; 19°F
Features patent-pending 3D NanoShell technology. Most versatile sleeping bag, featuring all of Sea to Summit's advancements in sleeping bag design.