Weighing just 5.6 ounces in size medium, packing down to the size of an apple, and totally impervious to rain while also breathing tremendously well, the Sitka Vapor SD jacket ($299) is the best ultralight hardshell jacket available for 2018.
It’s the Gore-Tex ShakeDry fabric that makes all that possible. Where traditional waterproof-breathable fabrics sandwich a thin, fragile membrane between an inner and outer layer of fabric for protection, ShakeDry employs a more robust membrane that can go without the outer face, making the top more breathable and lightweight.
Remember how water used to bead up and run off your old Gore-Tex shell when you first got it, but after years of use, it now soaks in and makes the jacket clammy inside? That’s because the DWR coatings used on the exterior face of three-layers never really lived up to the “durable” part of their name. And once they were destroyed by abrasion, weather, and body oils, the now-damaged DWRs allowed that outer layer to fill up with water, blocking the internal membrane from breathing, and causing your sweat vapor to collect inside the jacket.
ShakeDry, with its more durable membrane, permanently retains the ability to stop water on its outmost surface—causing it to bead up and run off. That means you can simply shake a wet ShakeDry jacket to knock the water off (hence the name).
Sitka, which, like Gore-Tex, is a division of W.L. Gore, maximizes the benefits of ShakeDry by endowing the jacket with a minimal but smartly-chosen feature set. Both the cuffs and hood perimeter are wrapped in elastic, rather than velcro or drawcords, to cut weight and maximize packability. The jacket is cut close to fit an athletic body, yet allows full arm articulation without exposing your waistline. A thin drawcord with a single toggle allows you to cinch the rear of the hood down over your head or loosen it to fit over a puffy mid-layer. The YKK zips are robust and extend to the hand pockets, giving you a secure place to store essentials. Because the ShakeDry membrane is black, the jacket only comes in black.
Unlike its arch-rival—Polartec NeoShell—which remains the most breathable waterproof-breathable membrane on the market, ShakeDry is fully windproof. That means ShakeDry doesn’t passively flow air like NeoShell, and isn’t quite as breathable as a result, but in my testing, the two technologies feel very similar as exertion levels rise. The imperviousness to wind also means ShakeDry will be the better option for staying warm through cold nights in the mountains.
As a technical note, there are no industry standards for measuring fabric breathability, and it’s very hard to objectively compare one membrane to another as a result. Gore is particularly reluctant to release any metrics, but it does claim that ShakeDry is currently its most-breathable waterproof membrane.
Sitka—a hunting brand—advertises the Vapor SD as “an insurance policy for stormy skies,” emphasizing its weight and packability over its performance. But while it’s not as feature-rich or as quiet as other Sitka hardshells, and while the thinner fabric won’t stand up quite as well to abuse, I think it’s an ideal primary hardshell for summer adventures.
Ultralight backpackers in particular should really appreciate the jacket’s incredible packability and small ounce count, while benefiting from more, not less, weather protection than they’re used to from similarly minimalist shells. The fabric is reasonably robust for activities that don't involve belly crawling through dense brush, and its excellent breathability pairs well with the total wind blocking when using the jacket as part of a layering system. It works great over a lightweight merino t-shirt during high exertion activities in chilly, wet weather, and helps get the most out of an ultralight down sweater when nighttime temperatures drop a little more than expected. All in a package you can shove in the pocket of your cargo pants with room to spare.