Rab Mythic Ultra Down Jacket - lightweight duvet with heavyweight warmth Review

© Dan Bailey

Stuffed with lofty 900 fill power down, and featuring a heat-reflective 'TILT' layer, the Mythic Ultra Down Jacket offers a lot of insulation for not much weight. It's a "game changer for mountain athletes, outdoor professionals, and fast-moving alpinists", Rab say, but while I'm none of those things, and I'd be instinctively sceptical of such bold claims anyway, I do know a quality jacket when I see it. If you're willing to invest a substantial wodge of cash for seriously packable performance, then the Mythic Ultra is quite something.

We got a first look at it towards the tail end of last winter (see vid), and really liked what we saw. It then sat in my review filing heap for several months, until the return of cold conditions could see it pressed into regular service again. This isn't a jacket for cool-ish weather; you really need things icy!


Light, very warm for its weight, and with a superb cut


Challenging price tag; hood can feel floppy with no helmet

Lovely long cut for maximum warmth  © Dan Bailey
Lovely long cut for maximum warmth
© Dan Bailey

Who and what is it for?

The rarefied set of folk Rab describes would, I'm sure, get on well with it; but this jacket isn't just for pros, wads and those aspiring to such heights. Out on a snowy summit or a frigid bivvy, who doesn't want something as warm as possible for as little weight as they can carry? On cold, dry Scottish winter hillwalking and mountaineering days (they do happen) I've been very glad of the Mythic Ultra, and it's been invaluable for winter camping too. Though I wouldn't choose a down duvet as a crap-hits-the-fan Scottish winter mountain belay refuge, in anything but settled high-pressure weather, I can see it doing well for winter crag trips, boulderers, and continental style valley ice climbing. Weight-conscious alpine climbers should take a look too.

For something this warm it packs down pretty darn small  © Dan Bailey
For something this warm it packs down pretty darn small
© Dan Bailey

Weight and warmth

"Our goal was to create an alpine down jacket with our best ever warmth to weight ratio" say Rab; so have they succeeded? Well at just 506g in my size L, plus 9g for the ultralight stuff sack (Rab offer a conservative 537g for size M) the Mythic Ultra is clearly way down at the lighter end of the scale for a full-on winter/alpine down jacket. It's also very, very warm. Try climbing or walking uphill in this jacket in typical UK winter temperatures and you'll quickly get too hot. For standing around in comfort I've not yet found its lower temperature limit. Warmer down jackets are available, and lighter alternatives can easily be had, but I suspect you'd struggle to find something that's both.

Forward, comrades, to sunlit uplands and snug, high collars  © Dan Bailey
Forward, comrades, to sunlit uplands and snug, high collars
© Dan Bailey


The Mythic Ultra Down Jacket comes in both men's and women's models. It's roomy enough to fit over a couple of midlayers, but I don't find it quite as spacious as a dedicated belay jacket and wouldn't tend to wear it on top of a shell (though I have). It's pretty puffy on the outside, so I don't think you'd want to try fitting a shell over it either; this is a stand-alone thing.

For maximum warmth around the midriff there's loads of length in the hem, and pretty much full bum coverage; as someone who's forever annoyed by shorter hems I find this great, as there's no question it makes for a warmer jacket. Hem drawcords help keep a nice seal, with elastic tails that tuck up inside to prevent snagging.

I would rarely want to actually climb in a down jacket (no plans to do Denali), but while many duvets don't seem to be cut with movement in mind in any case, the Mythic Ultra is an exception. Thanks to its active tailoring, arm movement is completely free, and I get little hem lift when my arms are raised. If you wanted to wear it for climbing, then the only limit I can see would be the relative vulnerability of its thin face fabric. The elasticated cuffs fit closely around the wrist, but are still roomy enough to go over bulky gloves. Overall, then, I find the cut pretty near perfect.

Cuffs fit easily over big gloves  © Dan Bailey
Cuffs fit easily over big gloves
© Dan Bailey


Rab's attention to tailoring is also apparent in the hood, which is sized to comfortably fit over a climbing helmet without significantly restricting head movement. As a result this is a jacket you could happily belay in - more than I can say for many insulated jackets I've tried over the years.

With cord locks concealed in the hem, and elastic tails channelled inside where they can't whip you in the eye, the hood pulls snug around the face, while the high collar (with a big fleecy chin guard) completely protects the neck and lower face. For added weather-shedding there's a little brim, but while this works well with the dome of a helmet underneath, or at the very least a hat for added bulk, on a bare head the peak can pull down over your eyes when the side elastic is tightened. The answer is to wear the hood loose. An additional rear 'halo' adjuster might have helped rein in hood volume for helmet-free use (ie. most of the time, for most of us).

The hood is very toasty  © Dan Bailey
The hood is very toasty
© Dan Bailey

Fill and construction

Filled with 900FP European Goose Down, the Mythic Ultra cuts no corners in terms of quality insulation. The higher the fill power the greater the loft and insulating performance, and for a mass market jacket this is about as good as it gets. There's plenty of the fluffy stuff, too - a generous 240g of it in a size M jacket. The down has been treated with a Nikwax fluorocarbon-free hydrophobic finish, which should in theory help prevent it clumping and thus maintain its performance when things get damp through sweat, condensation, or the elements (not everyone is convinced by hydrophobic down treatments, but Rab clearly believe in them).

All that down is only of use if it's distributed optimally, and to that end the baffle construction is key to a jacket's performance. Here Rab have gone for stitch through-baffles on the arms and hood - a lighter, easier-to-produce option that also gives you greater mobility where needed. Around the core, on the other hand, it's the warmer but more expensive boxwall style that helps the down loft properly. These baffles are offset, reducing the cold spots you'd otherwise get at seams.

Just the thing for a cold dark camp  © Dan Bailey
Just the thing for a cold dark camp
© Dan Bailey

Boosting the conventional insulation is a heat-reflective layer, sewn into the all important torso area of the jacket to help retain core warmth. A gauze-like aluminium-infused sheet that bounces back up to 15% of radiant body heat, this TILT (Thermo Ionic Lining Technology) scrim adds almost nothing in weight or bulk, but experience suggests it does make a difference to performance. While it's impossible for the end user to evaluate objectively, I do find this jacket surprisingly toasty for its marginal weight. Already used in some Rab sleeping bags, this is the first time that TILT has found its way into a garment - and I hope it's not the last.

Absolutely perishing outside; comfortably warm inside  © Dan Bailey
Absolutely perishing outside; comfortably warm inside
© Dan Bailey


To save weight it's a 10D Pertex Quantum fabric inside and out. This recycled ripstop nylon is tissue-thin, at only 28g/m2, and while I wouldn't like to get on the wrong side of too many rocks it does seem tough for its weight. Being light enough to allow the down inside to fully loft, the fabric is also effectively down-proof (I've had no escaped wisps yet), and seems pretty darn wind-resistant. There's a degree of moisture resistance too - always welcome in an insulated jacket - thanks to a fluorocarbon-free DWR.


Featuring twin zippers for easier access to your harness or under-layers, and an anti-snag draught-beating baffle, the main zip feels good and robust. Lighter concealed zips access the two hand-warmer pockets, which are big enough for gloves or a hat. You also get a roomy single chest pocket, and since this is cut into the insulation it's a good place to keep your phone warm. No inner pockets are provided, and though some users might like a drop pocket for their gloves I can't say I've missed it.

A good choice on a cold, dry mountaineering day  © Dave Saunders
A good choice on a cold, dry mountaineering day
© Dave Saunders

Ethics and environment

RDS-certified down and 100% recycled fabrics bolster the Mythic Ultra's ethical and environmental credentials. Rab is also a member of Fair Wear.

Close competitor - Mythic Ultra versus ME Kryos

In terms of warmth, remit, and price, the Mythic Ultra has obvious overlap with Mountain Equipment's Kryos, a jacket we reviewed back in 2021. They even share a similar look. So which would better suit you?

Well the Kryos weighs considerably more, so if weight is the final decider that may swing you to the Mythic Ultra. In terms of fill, you get a very similar quantity of down and a hybrid baffle construction in each, though it's a slightly higher grade 900FP from Rab versus Mountain Equipment's 800FP. But how does that equate to warmth? In my opinion they're pretty evenly matched here, though the Mythic Ultra may just edge it.

With the Mythic Ultra the big story is probably that hidden TILT layer, while the Kryos wears its distinction on its sleeve in the form of an outer face of weather-shedding Gore-Tex Infinium fabric. Thanks to this I think the Kryos feels tougher and more protective in foul conditions.

If I wanted a down jacket for Scottish winter climbing (I mostly don't, but there are times...) then the Kryos would win it; on the other hand, the fact that the Mythic Ultra offers similar or better warmth for quite a bit less weight gives it an obvious advantage for weight-critical uses - especially in cold, dry environments. Ultimately they're both fantastic!

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