Gear Review: Mammut Felsturm Half-Zip

Made with Gore-Tex Active Shell this breathable jacket was wearable in a wide range of temperatures.

>> The membrane Gore-Tex Active Shell. Like the original stuff, it’s expanded polytetrafluoroethylene (PTFE), but this new version is about 50 percent thinner and lighter, plus Gore devised a way to attach the liner fabric using less glue. A non-porous polyurethane (PU) coating protects the membrane from sweat and dirt. The PU also renders the fabric 100-percent windproof (unlike the others in this test, which allow a tiny bit of air to pass through). The hydrophylic (water-attracting) PU draws moisture in, then it’s pushed out through the membrane’s pores by your body’s heat output. The process requires a climate differential between the inside and outside of the shell, which is created by a buildup of humidity and temperature. In simple terms: You work, it breathes.

>>The claim Gore won’t say how much more breathable Active Shell is than previous membranes (nor would it provide a close-up image of the membrane itself), but our testers estimate it to be 20 to 30 percent. A key to that improvement: Gore developed a new lab test using a heated/sweating mannequin, so designers could study “whole body breathability”—not just the breathability of fabric swatches. Gore also works closely with manufacturers to streamline pockets, flaps, and excess lining materials that could hinder breathability.

>> The jacket “Unparalleled temperature range,” says one tester of this minimalist, half-zip pullover. The Felsturm is built with light, supple, fairly open-weave 20-denier nylon and a light tricot liner that result in unsurpassed breathability, negligible weight, and a tiny packed size. “On a ski tour up Utah’s 10,719-foot Lake Peak, it was raining at the trailhead, then sleeting and snowing all day,” says one tester. “Everyone else was constantly swapping layers, but I wore this from start to finish.” Clincher: He didn’t touch the Felsturm’s pit zips all day (though testers appreciated them on warmer trips). The great-fitting hood accommodates helmets, yet cinches well around the cheeks; it sealed out the chill even when ridgetop winds hit 50 mph. Most other features are sacrificed for weight (there’s only one Napoleon pocket). And Mammut sews the smooth-running waterproof zipper coils straight to the shell, trimming the standard strip of tape. The short cut is harness-friendly and loose enough to fit midlayers.

>> Same technology/costs less Scott USA Crusair Active Shell Jacket ($300, 12.2 oz.,

Price $390

Weight 10.5 oz.

Sizes unisex XS-XL