We can't say that the Rab Nimbus is a warmer version of our Editors' Choice Award winner, the Rab Xenon X, but it does share some of the same features that make the Xenon one of our all-time favorites. The Nimbus packs away just as easily, it layers great under a hardshell, and it has excellent weather resistance for a non-waterproof jacket. What distinguishes it from the Xenon is its superior warmth and additional weight. If you're a fan of the Xenon (like we are) but you run a little cold, the Nimbus deserves a place in your climbing pack, clipped to your harness, or on your back at the belay.
Rab Nimbus Review
Cons: Heavy compared with other models, hood doesn't quite fit over a helmet
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Our Analysis and Test Results
The Nimbus reminds us a lot of the Patagonia Nano Puff with its baffles and packability, except it stows away more efficiently in its oversized pocket, and it's much warmer. While the Patagonia Hyper Puff is warmer, it's three ounces heavier and less packable. The Nimbus hits a sweet spot between not-warm-enough and too-heavy.
The Nimbus uses a synthetic insulator called Cirrus, which has a fiber length that allows the material to re-loft better than other synthetic insulators. According to Rab, Cirrus insulation has the fill power equivalent of 600-fill power duck down and doesn't lose it's loft when it gets wet. In our experience, the Nimbus has one of the best warm-to-weight ratios of any synthetic jacket out there. We wore this jacket alongside the Rab Microlight Alpine Jacket (a down jacket) and found that is was less warm, more weather resistant, and only .8 oz heavier. Pretty good for a synthetic jacket.
Weight & Compressability
The Nimbus tips the scale at 14.6 oz, one of the heavier entries in our review. One of the main reasons the Rab Xenon X has remained our favorite for so long is for its balance of weight, warmth, and durability, all in an 11 oz package. While the Nimbus can't compete in the ultralight race with jackets like the 8.15 oz Patagonia Micro Puff, it's much more durable. We climbed our fair share of offwidths and squeeze chimneys in the Nimbus, and it's somehow still going strong, while the Micro Puff got shredded after a few pitches. Like the Xenon, the pocket that the Nimbus stuffs into is generously sized, making it very easy to pack away.
The Nimbus is more form-fitting than the same sized Xenon X. This makes it a more efficient insulator and a better mid layer, but the tighter fit doesn't feel as comfortable as the Xenon. We also feel that the hood is too tight to wear comfortably over a helmet. The hood does feel comfy on our heads stay in place without obstructing our vision. The Nimbus's hem is long, so it offers some extra warmth and coverage and stays nicely under the waistbelt strap on a backpack or a climbing harness. Two handwarmer pockets offer a warm respite for chilly hands, and there is a small internal chest pocket for important items.
While we're aren't gutting these jackets and getting our eyes on the stuffing to compare the re-loft times of Polartec Alpha to Cirrus insulation, we can say that standing in the shower with a brand new Nimbus, we stayed dry. These jackets don't have a waterproof membrane and rely solely on their DWR treatment to stay dry. These treatments become less effective as the jackets get dirty. Anecdotally, one of our testers was caught in a downpour for a few minutes before getting in his tent to go to sleep. He stuffed his slightly damp Nimbus into the bottom of his sleeping bag, figuring that at least it would be warm, if not dry when he put it on in the morning. The next morning it was warm and dried out within 20 minutes while making breakfast in the sun.
The Nimbus isn't incredibly breathable. On cold and windy climbs, we don't think the lack of breathability is a problem, but steep hikes and long approaches, we had to take this jacket off because we'd overheat. For a jacket that breathes and insulates, have a look at the Patagonia Nano-Air Hoody or the durable Arcteryx Proton Hoody.
The Nimbus looks a lot like a down puffy, and many of our friends confused it for a down jacket. It has the look of a technical jacket (which it is), and in our eyes, this detracts from its style, but that's why style is only 5% of our rating system. We can tell you this: if you pull out the Nimbus on a cold and windy day belay, you'll love its warmth, and you won't care what it looks like.
The Nimbus is a great belay jacket and an awesome water resistant mid layer. We highly recommend it for anyone adventuring in weather where it's cold, but not cold enough to snow, and down will leave you vulnerable to the cold rain. It doesn't have to be freezing out to get hypothermia.
With many jackets in this category coming in at $300, the Nimbus is a great value at $245. It easily competes with top offerings from Patagonia and Arc'teryx. We are impressed with its durability, something we feel is sorely lacking as jackets become lighter and lighter.
While this jacket didn't get an award, it still comes highly recommended! It's warmth-to-weight ratio, and durability make it a reliable partner, especially when the weather is looking squirrely. While it didn't perform as well as the Xenon X overall, it's an exceptional choice if a warmer option suits you.
— Matt Bento