It’s no secret that wool is huge right now. Long consigned to woodsy cabin blankets and itchy Christmas sweaters, the age-old material has come into its own in the past decade thanks to modern treatment techniques and clothing design that have all but eliminated the itch and given it a sleeker, more athletic cut than the boxy garments of old. The real breakthrough in wool was the use of merino, the hair from a breed of mountain-dwelling sheep in New Zealand’s Southern Alps. This region also happens to be the home of Icebreaker, a brand that has made full use of the fur from the country’s most populous residents. We’ve been wearing Icebreaker’s Sierra Long Sleeve Zip jacket ($180) all summer and fall for mountain hiking — and though merino sheep have a few more centuries of wear-testing on their coats than we ever will, we’ve managed to form some opinions of our own.

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Aside from the feel-good perspective of wearing something that’s not made from petroleum, wool has two distinct advantages over synthetic fiber fleece: it stays warm when it’s wet, and it doesn’t retain odor (though have you sniffed a sheep lately?). In a soaking rain in the Canadian Rockies, we pulled on the Sierra jacket as a layer under a shell for added warmth and it provided just that, even one sweaty hour into a hike above treeline, where a chilly wind would have been serious trouble in a less insulating jacket.

As for its stink-free qualities, we proudly admit that we haven’t washed the jacket — ever. This is even after a summer in the mountains and more sweaty, steep, windy miles and vertical feet than we care to count. And guess what? It doesn’t smell at all. Mind you, this was all done in the name of thorough gear testing and doesn’t represent our general approach to hygiene.

The mid-layer fleece jacket field is crowded; like so many others of its ilk, the Sierra will probably find itself most often worn as a fall jacket in more urban environments. And that’s okay. Its styling straddles the city/trailhead divide more comfortably than most technical jackets. The merino is soft-brushed and sleek; the cut is trim and athletic, flattering the wearer; and the muted gray with yellow accents doesn’t broadcast that you’ve been wearing it on the trail all autumn — but it isn’t boring, either.

If the Sierra has any downsides, they’re slight ones. It’s a touch warm for a mid-layer, except in colder conditions; it would actually work better as an outer layer for cross-country skiing or winter running. The sleeves are a bit snug, making it difficult to pull on over a base layer. And though merino is the softest wool, those with very sensitive skin will still find it a tad itchy. All in all, though, this is a versatile jacket that earns its place in our pack for backcountry and urban outings alike. Sheep: pretty smart after all.