It won’t help you climb 26,289-foot Shishapangma in 10½ hours like Ueli Steck did, but if you’re into unburdened pursuits of any kind—as our tester found after three straight weeks on the John Muir Trail—this sub-one-pound bag surely won’t hurt. It’s one of seven components of Mountain Hardwear’s new Ueli Steck Alpine Speed Climbing kit, which ruthlessly cuts weight to aid his superhuman pace. The Mountain Speed is seven-plus ounces lighter than the company’s previous ultralight 32°F bag (the Phantom), a feat accomplished by upgrading some materials and eliminating others.
The upgrades include a proprietary shell fabric that’s ultralight yet tough and water-resistant and premium 850-fill power* down (penalty: cost), while the reductions come in the form of a half-length zipper and a markedly slim cut (penalties: minimized venting and access, and less roll-around comfort. It’s not for claustrophobes, but the compact shape delivers superior thermal efficiency and packability—the bag compresses down to the size of a typical puffy jacket. And our JMT tester says a comfortable face gasket and shaped footbox help offset the minimalist cut. Warmth? Spot on, thanks to a form-fitting hood that enhances insulation in freezing temps. One tester used it in the Andes and says, “I didn’t shiver at 29°F.” $400; 15.5 oz.; 32°F; mountainhardwear.com
*FILL POWER refers to the amount of space (in cubic inches) one ounce of fully lofted down consumes. A higher number equals loftier down that’s warmer for its weight.