Mountain Equipment Superflux Jacket Review

Synthetic 'down' insulation is bang on trend at the moment. Various new types of fill have come to the market recently, claiming to mimic more closely than ever the loft and warmth-for-weight of bird fluff, but without its wet weather and animal welfare drawbacks. Instead of coming as a sheet on a roll, like conventional synthetic insulation, the new down substitutes are loose, just like down, and that is key to their feel and performance.

Making use of 3M's Polarloft Featherless fill, the Superflux is Mountain Equipment's first foray into this style of insulation, and I think it's something of a success. This jacket is really pleasant to wear thanks to its fluffy loft and high warmth for minimal weight - in fact, if you didn't know better, you'd probably assume that the contents had been donated by a goose.

Ideal for a chilly day on Skye  © Dan Bailey
Ideal for a chilly day on Skye
© Dan Bailey


With a spacious cut that fits well over midlayers, the Superflux is best described as roomy rather than athletic. Its hem sits well below the waist, dropping lower at the rear to provide almost full bum coverage, so protection from the elements is exellent. In my experience a longer body is a hallmark of Mountain Equipment jackets, and testament to thought they put into keeping warm in the mountains. When climbing, this length in the hem helps keep it where you want it, securely in place under your harness; for the rare occasions when I might want to actually climb in a jacket this warm, that's good to know. Under-arm articulation is reasonable - there's no appreciable hem lift - but movement is not quite as unhindered as on some more technically-cut Mountain Equipment jackets such as the Prophet. In overall fit and feel, the Superflux seems rather more of a general-use jacket than a climbing-specific one.

The hood is simple, but spacious enough for a helmet if you don't mind restricted head movement  © Martin McKenna
The hood is simple, but spacious enough for a helmet if you don't mind restricted head movement
© Martin McKenna


The key question: is Polarloft Featherless noticeably better than more conventional synthetic insulation? Answer: yes, in certain situations I think so. But I wonder if it also imposes certain limits on garment design.

Mountain Equipment tell me they held off on offering down-like synthetic fill until something genuinely decent came along, and the Polarloft Featherless insulation they've developed in collaboration with 3M seems to be just that. This loose fill is blown into the jacket in the same manner as down, and just like down it has to be held in stitched-through baffles. Its loft is impressively down-like, compressing readily, fluffing back up instantly, and offering loads of warmth for its minimal weight (243g of fill in size L for a jacket weight of 535g). To the casual wearer it's pretty hard to tell the difference between this and the real thing; it feels lovely and soft to wear.

Offering a level of insulation that's said to be roughly equivalent to 700 fill power down, it must be among the best performing featherless fills currently available. By way of a synthetic comparison, meanwhile, the Superflux is a similar weight to Mountain Equipment's Primaloft Gold-stuffed Prophet jacket, but if anything feels marginally warmer. The exception to this would be in really minging Scottish winter-like conditions, where the profusion of stitched-through baffles on the Superflux would be a disadvantage.

Waiting for a Basteir Tooth photo op that never came - but at least I'm warm  © Dan Bailey
Waiting for a Basteir Tooth photo op that never came - but at least I'm warm
© Dan Bailey

Being loose fill rather than a sheet, Polarloft Featherless is in theory slightly more breathable than conventional synthetic insulation. This is hard to quantify in use, but my experience to date would seem to bear that out, and I've found the Superflux bearable to wear during moderate exertion (walking gently uphill, say) in moderately chilly autumn weather. On all but the coldest days I'd probably draw the line at actually climbing in it, but in terms of breathability it certainly beats the boil-in-the-bag feel of some of the more conventional synthetic jackets I've used over the years.

The bottom line? In terms of pure warmth-for-weight, the best quality down would still have a considerable edge over this fill. If you're expecting extreme cold, especially dry cold, then stick with feathers. But compared with a mid-quality down of about 700 fill power I've found that Polarloft Featherless does indeed come close. For less extreme cold, and especially in the wet, it has obvious advantages over down. And what's more, you dont feel you have to treat it with the respect you'd give your expensive down duvet. It is more easily washable, for instance. I think this is a useful addition to Mountain Equipment's synthetic insulated lineup, carving something of a niche all its own.

Like a real down jacket, it's perfect for hanging out at the crag  © Martin McKenna
Like a real down jacket, it's perfect for hanging out at the crag
© Martin McKenna

Outer fabric

At just 20 denier, the Drilite Loft outer fabric is pretty light stuff, but with a ripstop pattern it seems more than tough enough for general mountain use, and while I might not want to show it the inside of too many granite chimneys I have not yet made a mark on my review sample. It is highly windproof, and shrugs off a passing shower with ease, so mizzly damp autumn conditions have been no problem, and I've only needed to stick a waterproof shell over the top once the rain really starts.

Its Drilite Loft outer fabric feels pretty windproof  © Dan Bailey
Its Drilite Loft outer fabric feels pretty windproof
© Dan Bailey

A lack of seams over the shoulders and across the top of the arms increases its weather resistance for winter belays. These are the areas that are going to see the most spindrift, and take the brunt of any rain or drips. However, as I've already mentioned, just like down the loose fill has to be held in numerous small baffles, and thus the stitched-through quilted construction of the rest of the jacket leaves a lot of scope for moisture to get in. This is a key reason why I think the Superflux is only halfway to being a full-on, over-the-top winter belay jacket. When the crap really hits the fan, it's going to be better used as a midlayer under a waterproof. For full foul weather winter climbing duty, then, Mountain Equipment's existing and rather more weatherproof synthetic jackets, such as the Fitzroy and the Prophet, are still preferable.


Though it's definitely more of a generalist than a climbing specialist, the Superflux does still include a couple of techy-oriented features.

Double zipper provides easy harness access
© Martin McKenna

Dual tether drawcords
© UKC/UKH Gear

Backed with a little anti-snag storm flap, the main zip is a robust YKK Vislon, with a double zipper that allows easy access to your harness for belaying - a feature I've already used several times when cragging. Another nod to climbing use are the hem drawcords, which are two separate strands rather than a loop that you could accidentally clip into when racking gear. Small but important details like this are typical of Mountain Equipment. With no velcro tab for volume control, the wrist cuffs are simple elastic. On the plus side these are comfy and unfiddly; it can however be a bit of a struggle to squeeze them over the bulkiest gauntlets.

The two external hand pockets are huge, easily big enough to swallow ski gloves or an OS map. Positioned quite low on the body, they are partly covered by a harness or a rucksack hipbelt, but a useful amount of pocket remains accessible even then. A single large inside pocket gives you more than enough room for a phone or some cereal bars. One of the hand pockets doubles as a reversible storage pouch which you can clip to a harness; it's not a tiny bundle, but I guess respectably small for a jacket this warm. I'm sure Mountain Equipment didn't intend it, but I've found this doubles, too, as a mini pillow for camping.

Stuffed into its own reversible pocket  © UKC/UKH Gear
Stuffed into its own reversible pocket
© UKC/UKH Gear

Finally, the hood. This is spacious enough to fit over a helmet, but only just; with the zip done up head movement is limited. That's another reason why, although you can use the Superflux as a belay jacket, I'm not sure I would want to in foul weather. Lower face protection is good, keeping the chin covered. But with only a light elastic rim and no side drawcord adjustment, the seal around the face is not completely storm proof, while the lack of any stiffening on the brim means it can flap about in high wind. The single rear volume adjustment is effective at pulling the hood in close and warm around the head though. Overall it's a nice snug hood, and has simplicity in its favour. But ultimately, it feels more like the hood of a midlayer than the sort of helmet-friendly storm haven you'd get with one of Mountain Equipment's more climbing-focused synthetic jackets.

Simple elastic cuffs  © UKC/UKH Gear
Simple elastic cuffs
© UKC/UKH Gear

Two-way zipper  © UKC/UKH Gear
Two-way zipper
© UKC/UKH Gear


Polarloft Featherless:

With an impressively soft feel and a down-like springy loft, Polarloft Featherless really does feel like a viable alternative to mid-quality down, and roughly equates in performance terms to 700 fill power down. While its performace can't compare with the best quality down found in premium clothing designed for the lowest temperatures, its advantage in less extreme cold is that it goes on working well when wet. It packs down small, and being synthetic does not need to be treated with the respect you might give a down jacket. In use, this blown insulation feels a little more breathable than some conventional synthetic fills, though I'd stress that this is anecdotal, and I've not yet put it to the test in a full range of conditions year-round.

Superflux jacket:

At £200 the Superflux is not cheap, but that's a ballpark price for quality synthetic insulation, and seems more than reasonable for this brand new, almost-as-good-as-down fill. With its simple cut and less mountain-specific feature set, this jacket is a good all-rounder, but feels less climbing-focused than some of Mountain Equipment's other synthetic offerings, and lacks a few refinements that you might miss in a Cairngorm storm. It is roomy and warm enough to do duty as a winter belay jacket, but while the Drilite Loft outer fabric offers plenty of weather resistance the multiple stitched-through baffles would slightly compromise the performance in foul conditions. If you're expecting the worst then alternatives from Mountain Equipment such as the Fitzroy or the Prophet would still be a better bet. For the full range of winter climbing conditions, the Superflux is perhaps better employed as a very warm midlayer than an over-the-top outer. However for general day to day use, hillwalking or belaying at the crag, the Superflux is all the synthetic insulated jacket you'll need. I'd love to see Polarloft Featherless insulation married to a more climbing-oriented, all-weather design though. Would the quilted construction necessitated by this type of loose fill make that a tall order? Mountain Equipment, the ball's in your court.

Mountain Equipment say:

Superb all-weather insulation; combining breathability and protection in a single versatile layer.

3M® Polarloft® Featherless insulation not only works wet or dry but, thanks to its blown construction, breathes effortlessly as well. Combined with our highly protective DRILITE® Loft outer and seamless shoulder construction the Superflux is a jacket that thrives as an outer or mid-layer in the most difficult mountain conditions.

  • Price: £200
  • Sizes: S - XXL (men's only)
  • Weight: 535g (size L - our measure)
  • Drilite® Loft 20D outer fabric; totally windproof, exceptionally light, highly breathable and water resistant shell fabric used to protect down inside sleeping bags and clothing.
  • 243g (Size L) of Polarloft® Featherless insulation by 3M®: Synthetic insulation that offers an excellent warmth-to-weight ratio and small pack size.
  • Stitched-through quilted construction in the body
  • Adjustable Elastane bound Mountain Hood
  • Shoulder Shield construction
  • 2-way YKK® moulded centre front zip
  • 2 zipped hand warmer pockets
  • Internal zipped security pocket
  • Elastane bound cuffs and dual tether hem drawcords
  • Packs into hand pocket with twin karabiner carry loops

For more info see

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31 Oct, 2017
Two things I'd like to know: 1) Why do UKC product reviewers extraordinaire Bailey and Archer always look so damn miserable in review photos? 2) Is there a clumping effect with synthetic down when it gets damp? If so does this impair performance over a traditional synthetic insulation? Finally how does it compare with hydrophobic down.
31 Oct, 2017
What would the product be like if they stuffed it in a Fitzroy?
1 Nov, 2017
Dan is smiling in one of the photos! And for my part, particularly when i set up a photo using self timer I feel a complete tit then grinning at the camera! :-)
1 Nov, 2017
Blown fills like Polarloft Featherless do indeed change the parameters when it comes to designing a garment. When it comes to traditional synthetic wadding like Primaloft etc. it is simply sewn into a garment like a fabric. With Featherless, however, just like down it has to be kept in baffles to avoid shifting around inside the jacket. One difference versus down, though, is that our research has shown that with synthetic featherless those baffles need to be relatively small (even smaller than if you were using down). This clearly presents design limitations. We agree with Dan regarding use of the jacket: the stitch lines on the Superflux means that in really difficult conditions (damp, freezing, riming) this type of product will not offer such good protection, or function as well as an overlayer such as our practically waterproof Prophet jacket or as our highly water resistant Fitzroy and Citadel jackets. On the plus side it is infinitely softer and more comfortable to wear especially as a mid-layer, meaning that in all but the most testing of conditions it is probably a better all-round option. We could certainly make an all-out ‘belay jacket’ with Polarloft Featherless. Basically we’d continue the construction method used on the shoulder yoke to the rest of the jacket, and beef up a few of the other features. It’s something we’ve looked at doing but whether the advantages of this construction would really count in the world of a belay jacket is open to argument in our view. Addressing the forum’s questions… 1) Clumping of blown synthetic fills doesn’t happen as it might with down. In normal use you’re unlikely to make it turn to those hard little balls that down eventually forms once completely drenched, but it might with the cheapest blown synthetics just because the fibres and interactions between them are so weak. We tested a lot of options before coming out with Polarloft Featherless and were unimpressed by many of them. Some clumped readily, some were almost impossible to put into a garment evenly, some just weren’t very warm, and some were great for a while but then disintegrated after about ten cycles through the washing machine. Some were ruined after less than 5 wash cycles. So, yes some blown synthetics can clump but this one certainly shouldn’t. 2) Hydrophobic down differs quite a bit to blown synthetics. Down remains the be-all and end-all when it comes to warmth to weight ratio, and we may never match it, for reasons discussed here: However down, whether coated with a hydrophobic treatment or not, is inferior in really wet conditions to synthetic insulations. We at ME use hydrophobic down in a few of our products, generally relatively lightweight jackets which have shell fabrics with no water resistant coating. We use it there because the jackets are likely to be used in mixed conditions, often above freezing where rain might be encountered, and because it gives them half a chance of fighting off a short sharp shower. However, hydrophobic down isn’t fundamentally different to down in that once that repellent coating has been penetrated it will still get very wet and will still clump together in the way that synthetics shouldn’t. We don’t use hydrophobic down in our other products (warmer jackets, sleeping bags) for various reasons. Firstly the coating has a relatively low lifespan (it’s effectively DWR for feathers; we know how quickly DWRs become less effective). Also, hydrophobic down doesn’t fundamentally change the way a down product can be used: it’s still no use in prolonged wet conditions, and if you’re going out in the pouring rain then down probably isn’t the best option!. Hydrophobic down is also less effective at dealing with moisture than using a shell fabric with a water repellent coating which will last the lifetime of the product, and there are various other design things you can do to massively increase the water repellence of down without using a coating. Finally, we aren’t a big fan of taking a natural product like down, removing the natural repellence of the feathers so they don’t smell and clump together, and then sticking on man-made repellents which we as an industry are trying to move away from. So in short, blown synthetics like Polarloft Featherless are better in wet weather than down but don’t provide as much insulation for their weight. They’re less durable over very long term use, but they’re easier to care for than down and a bit more tolerating of rough use. 3) We could make a Fitzroy using Polarloft Featherless and could make it look outwardly the same. However, ‘under the bonnet’ for reasons discussed above, it would be very different. It’d be pretty difficult to construct but we like a challenge! In terms of performance we’d expect similar weight and warmth with marginally improved breathability, but greater softness and wearability. It might cost a fair bit but we wouldn’t be sure until we do further design work. Sorry for the monster post. Dr Matthew Fuller, Product Engineer at Mountain Equipment
That's not misery - it's just my default farting-around-with-camera-timers-and-remote-triggers face. Inside I'm smiling. Plus, like Toby says, if I try to force a grin I feel like an eedjit and it ends up looking more like a grimace anyway. As for the important questions, Dr Matt has covered them better than I could...
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