The Arc'teryx Alpha SL is a lightweight waterproof GORE-TEX® PacLite® jacket designed as a packable emergency storm layer for alpine use. Mine arrived just in time for a heavy spring shower, which provided an immediate test of the reason I had bought it.
Two years later, it had spent plenty of time hiking and biking around the Chamonix valley and beyond, along with a considerable amount of time compressed into a backpack. It remained waterproof in heavy rain and still looked much as it did when new. The jacket is simple by design, with two chest pockets, pit zips, adjustable hood and waist, and little else. It is not trying to be a feature-heavy shell.
The Speed Hood® is helmet compatible for climbing helmets, although I never used it with one. It has a useful peak and rear adjustment, both important in prolonged rain. A badly fitting hood without a peak can make an otherwise good waterproof jacket considerably less useful.
The Alpha SL is packable, but it still has enough substance to feel like a proper waterproof jacket when worn. I had previously used lighter shells for cycling and found that their small packed size came at the expense of protection. The Alpha SL strikes a better balance. It packs down when you need it to, but doesn't feel like you're wearing a plastic bag when the weather arrives.
The carbon colour with blue accents has also aged well. It is understated enough for everyday use, which matters when a jacket is going to last for years rather than a season.
My only real criticism is the short front. A little more length would improve protection when cycling or wearing it with ordinary trousers. The sleeves are a good length for me, despite having long arms, so sizing is worth considering carefully.
It is a straightforward jacket with a straightforward job: keep the weather out, pack away when it isn't needed, and survive being used properly. Two years in, it had done exactly that.