Montane Icarus Jacket Review

The Icarus is a synthetic-insulated jacket that uses a new fill called PrimaLoft ThermoPlume. This is said to be closer than traditional synthetic insulation to mimicking the properties and feel of down. We had a quick look at the Icarus in October (Sneak Preview), and it got a mention in our Top 10 products following the ISPO Trade Show back in February (UKC ISPO Top 10).

Promising near-down-like warmth-for-weight, but with the added bonus of wet weather performance and animal welfare, we felt it had to be worth a closer look. I have now been using the jacket for a much more extended period, testing it in the Pyrenees over the summer, back in the UK in varying weather conditions this autumn, and then in Spain on a climbing trip. I've worn the men's Icarus jacket, but the Women's Phoenix jacket is essentially the same only with a female cut to the design, so everything apart from the fit will apply to that jacket as well.

Montane Icarus Jacket  © UKC Gear
the Montane Icarus Jacket


The jacket is well cut for my body size, and I have a fairly standard climber's build. With a decent wide shoulder fit, and sleeves just the right length, it passes the test that you don't really notice it when on. This has become a quick go-to garment for me, and not just when out on the hill. The sleeves are relatively tight fitting - in my case not tight enough to contribute to any unwanted hem raise when lifiting my arms, but perhaps this might make the jacket feel constricting on chunkier upper bodies. This snug well tailored fit makes it ideal as part of a layering system, fitting well beneath a shell for instance. The flipside to this is of course that it functions less well as an over-the-top belay jacket, a use for which, to be fair, it's clearly not designed.

Montane Icarus Jacket - large helmet hood  © UKC Gear
The slightly boxy fit on the hood may not suit everyone

The hood is very basic, with no adjustment possibility, just an elasticated hem. My impression is this is quite a baggy fit since I normally take a very big hat size, so those with small heads should try the jacket first and pay attention to the hood sizing in particular. Even with my big head, there are a couple of square corners giving a slightly boxy look. That said, the fit feels pretty snug with the zip done up and it functions well in blustery conditions which is quite an achievement considering the lack of adjustment potential. Also missing is a waist drawcord, but this is in line with the minimal feature set on the Icarus.

Being minimally structured, the hood is designed as 'under helmet' if required. On reflection we reckon that's a good option for a jacket of this weight, while for a heavier over-the-top synthetic belay refuge we'd prefer an over-helmet hood.


Several down-like synthetic fills have come to the market recently. While they are all impressively fluffy, we think it's fair to say that none has yet stood out as a full replacement for higher quality down. The Icarus uses PrimaLoft's new ThermoPlume technology, a synthetic fill which is claimed to "come closest yet to mimicking the structure of down". Having felt this stuff at the ISPO trade show in January 2017, and now seen it perform in a jacket, I can confirm that it is indeed light and fluffy. However I think it still stops some way short of actually feeling like a down jacket. PrimaLoft ThermoPlume is said to offer insulation equivalent to 550 fill power down. Now while that might be an improvement on standard synthetic fills, it's not going to slug it out punch for punch with the 600, 700 or 800 fill power down you can expect to find in a top-end jacket. Round one to down then, which still offers more warmth for an equivalent weight - if you're able to pay the quality premium at least.

Compared to previous verisons of Primaloft, which came on a roll, ThermoPlume has a loose structure rather like down, and indeed it has to be blown into the jacket with the same equipment that the manufacturers use with down. One consequence of this loose structure is that the fill has to be held in place inside multiple stitched baffles. This helps give you something approximating the look and feel of a down jacket, but it also introduces a lot of stitching which makes for a less weatherproof garment (compared with, say, a traditional synthetic belay jacket).

On the plus side, one of the main benefits of these synthetic fills is their performance in the wet. Whilst I haven't yet been able to test it in a full mountain soaking, it has done well in the rainy and windy conditions I have managed and hasn't exhibited any of the 'clumping' you'd typically experience with down. Keeping it light and clump-free helps the Icarus maintain its warmth even when damp. That clearly has benefits for active mountain use in the rainy UK. Round two to synthetic, then.

The filling itself is described as "incredibly lightweight" in the marketing blurb. At around 580g (size L), the Icarus is only 40g lighter than the Flux Jacket, 100g heavier the the Quattro Fusion and around 150g heavier than the Featherlite Down, all from Montane. This doesn't make it "incredibly lightweight" in my book. In fact I'd go as far as to say that its weight is fairly middle of the road. Compared with the Scottish winter-oriented Flux Jacket, for instance, which we have reviewed on UKC/UKH in the past, the Icarus has fewer climbing-specific features but arguably offers marginally more by way of warmth. It's horses for courses, in other words.

The change in baffle size in the under arm area

Elasticated cuffs

The baffles are zoned cleverly for freer movement, with thinner sections under the arms and wider baffles on the central front, full back and the hood. This isn't going to keep you warm as things get really cold, but it isn't designed for that. As a stand-alone piece in more clement conditions, or as part of a layering system, it certainly performs to keep you warm even if it gets slightly damp. I did use it as a belay jacket in El Chorro and it functioned well, although there are probably better jackets designed specifically for this purpose.

Montane Icarus Jacket - as a belay jacket  © UKC Gear
Use it as a belay jacket for cragging, or as a midlayer piece in colder conditions

Outer fabric

The outer fabric is made from reliable Pertex® Quantum although in this case it gets the 'Eco' tag as well since it is made from 100% recycled materials - a thumbs up from us. Pertex Quantum is windproof and water resistant and pretty tough all round. It comes in three colours - orange, navy and grey - nice, but another brighter one would have been good (think photography). The Women's Phoenix model comes in some attractive subtle aqua and berry colours as well as black. The lining is made from the silky smooth 100% recycled PEAQ fabric which is breathable and fast drying and feels good against the skin.


The original poor YKK zip - now upgraded on new models

Handy outer hanging tab

The Icarus comes with a pretty minimal feature set which is in line with its stated aim of simple and lightweight. The pockets are placed high to allow use under a harness, and while they come with zip fasteners they do have the disadvantage of being really quite small. You will struggle to stuff a pair of gloves in a single pocket, though they do have a deep cut which makes them good for safely carrying small things like wallets, phones or car keys but not good for keeping your hands warm. When you look at the jacket it is obvious why the pockets are small since they are positioned in line with the change in baffle construction which means that they are more central than many pockets. If used as part of a layering system then you will probably have other pockets in which to put your gloves and the small and secure pockets on this one may well be useful for other things.

Montane Icarus Jacket - decent Napoleon pocket  © UKC Gear
Montane Icarus Jacket - decent Napoleon pocket
© UKC Gear

The front zip is a coil YKK zip and not the significantly more solid chunky plastic YKK zips found on other Montane jackets like the Flux and Quattro Fusion. On the test jacket we had, the zip malfunctioned relatively quickly and looks like it won't last much longer. We informed Montane of this and they told us:

"We identified some issues with the zippers used on the original garments. Unfortunately some of the zippers delivered from YKK were faulty. This has been resolved now and we have switched the zippers going forwards to a sturdier zip."

So hopefully this very problematic issue has now been resolved.

The Icarus is styled as being "designed as a very lightweight, simple, packable insulation jacket..". Well it is packable in the sense that you can pack any garment by cramming it into your sack, but there is nothing else that makes it particularly 'packable'. It doesn't fit inside a reversed Napoleon pocket, it doesn't come with a stuff sack, and it doesn't compress anything like as much as a down jacket. However it is robust and doesn't suffer from a bit of rough treatment stuffing into a sack; just don't assume that it will go as small as the equivalent weight down jacket.

There is one Napoleon pocket with zip but no internal pockets. There are no drawcords anywhere on the jacket, while down at the cuffs the simple elastic keeps bulk to a minimum around the wrists. It also features the customary and welcome outer hanging tab. This minimal feature set though should not be seen as a negative since the jacket aims to be simple, sleek and part of a layering system; and it should be reiterated that the fit is good in spite of the lack of adjustment potential.


Neither an ultralight specialist, nor a super warm alpine/winter belay jacket, the Icarus is best considered a general outdoor all-rounder. At £140 it is a very decent price for a jacket of this quality, but for a tenner more you can get a higher specced Flux, and for £40 more a significantly warmer, lighter and more compressible Featherlite Down jacket, both from Montane. The use of a new fill technology needs to be applauded, and time will tell if this really is the down replacement to give a long-lasting solution. However the 'packable lightweight' claims seem to be misplaced here since it simply isn't that light or packable for such a minimalist jacket.

Having said that, these reservations are mainly aimed at the marketing blurb since the jacket you get actually performs very well and I do find myself choosing it more often than not from my (quite large) collection of lightweight insulated jackets. It has a very nice feel about it and, with the caveat of it hopefully now having a better zip than the version I have, I do find myself liking the jacket very much overall. At £140, it represents good value for anyone looking for a simple light-ish jacket for use as part of a layering system - just don't think that you are getting a 'virtually-as-good-as-down' jacket.

Montane say:

Employing innovative new PrimaLoft® ThermoPlume technology, a new synthetic fill which comes closest yet to mimicking the structure of down to provide an incredibly lightweight and warm insulation package, yet with the advantage of performing even in wet or damp conditions.

  • Price: £140
  • Weight: 584g (size L - our measure)
  • Sizes: S - XXL (men's sizing only - the women's version is the Phoenix)
  • Fill: PrimaLoft® ThermoPlume synthetic fill equivalent to 550+ fill power down
  • Designed as a very lightweight, simple, packable insulation jacket which is perfect for layering or can be worn standalone
  • Micro baffle construction allows for close body fit and dynamic freedom of movement
  • Articulated arms for high reach movement, tailored specifically to prevent hem lift
  • Hood is designed to be worn comfortably under a climbing helmet
  • Two hand pockets with YKK reverse coil zips positioned clear of a backpack hip belt or climbing harness
  • Concealed zipped chest pocket
  • Full length YKK reverse coil front zip
  • Internal storm guard behind centre front zip to prevent weather entry
  • Roll over chin guard lined with brushed microfleece for comfort next to the mouth and chin
  • Low bulk cuffs with internal lycra closure
  • Elasticated hem to prevent spindrift entry and heat loss
  • External rear Montane hang loop

For more info see

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