Rab Cirrus Flex 2.0 Jacket and Cirrus Flex 2.0 Hoody  Review

© Rob Greenwood

I'm not sure when the term 'active insulation' was coined, but the principle of a warm jacket you can use on the move, but not get too sweaty in, is a fine line to tread. Breathability is key, as is the amount of insulation: too little of the former and too much of the latter and hey presto - you've got yourself an extremely sweaty jacket. Balance is essential, and that's what we'll be looking for in this review. 

Our Gear Editor Dan reviewed the Cirrus Flex Vest last year, and got on really well with it; in fact he still practically lives in it:

But what are the sleeved versions like?


As midweight synthetic insulated jackets, the Cirrus Flex 2.0 Jacket (£115) and the Cirrus Flex 2.0 Hoody (£130) are designed for on-the-move activity throughout the cooler months of the year, or as an insulated piece in the warmer months. The limiting factor as far as warmth is concerned are the ventilated side panels, which allow air to flow through. Thanks to these it's unlikely you're going to want it as an outright belay jacket in cold conditions, as this level of breathability isn't what you want to keep you warm (in this case you'd be better off be getting the Cirrus Jacket or Cirrus Hooded Jacket sans 'Flex'); however, it's this air that enables you to wear it whilst on the go without expiring through heat exhaustion.

Endlessly traversing Minus Ten at Stoney Middleton, early in the season, on a particualrly cold/bright day  © UKC Gear
Endlessly traversing Minus Ten at Stoney Middleton, early in the season, on a particualrly cold/bright day
© UKC Gear

So where do we see it being used? From a hillwalkers perspective it's probably of most interest for walking on colder days from autumn, to winter and on into spring. The fact that it features synthetic insulation means that you don't have to worry about whether or not it's getting too wet, because - at least in theory - it'll keep you warm when wet (although I'd always argue that if it is raining, you're probably best off wearing a waterproof - especially whilst walking). Its active cut makes it ideal for scrambling too, with excellent freedom of movement.

For climbers it's probably best to make a distinction between climbers who are interested in rock, and mountaineers who are interested in Scottish Winter and the alpine environment. 

Cirrus Flex at Stoney  © UKC Gear
Cirrus Flex at Stoney
© UKC Gear

Fewer things make you sweat more than carrying a 13kg child  © UKC Gear
Fewer things make you sweat more than carrying a 13kg child
© UKC Gear

Rock - I've used the Cirrus Flex 2.0 whilst bouldering, sport climbing and trad climbing throughout the cooler months. Its cut (which we'll come onto shortly) being as good as it is, it's great to climb in, with the only caveat being that for sport and trad, it'd have to be pretty cold in order for you want to wear it, and those times that I did my hands were really, really cold. As such, it might be of more interest as a belay jacket, but - and this is a big but - it's worth highlighting again that whilst it can be used as a belay jacket, its breathable nature means that it's at the cooler end of the spectrum.

Mountaineering - This is a very natural setting for the Cirrus Flex 2.0, not least because the weather is (hopefully) cold enough to really make the most of both its insulation and its breathability. This could, particularly on cold days, be something I could see myself walking in wearing, with a base layer underneath, then boosting it with another fleece layer before starting out climbing. This would work both in Scottish winter and the Alps, and the benefit of using it in the former is the fact that its synthetic nature deals with the naturally warm/wet environment that curses/blesses our shores.



The sizing on the Men's Jacket is spot on, particularly when compared to the women's, with a medium being very much a medium. When it comes to the fit, it's definitely on the slimmer, active side, but it's so well cut so that this doesn't interfere with its freedom of movement. The classic 'lift test' yields very little movement in the hem whilst waving your arms around. Basic though it is, this is a great indication of what it's going to be like climbing, scrambling or mountaineering.


Before commenting on the fit, it's worth commenting on the sizing, which is - at least in our opinion - one size out. As such, if you're usually a 10 you'll likely be a 12 here, unless you like your clothing really, really tight (we had to send our first size back as a result of this).

Once you've got the right size, the fit is pretty flawless. It's got regular cut around the waist (not too long, not too short) and a good length in the arms, but most important of all is that much like the men's jacket there's little or no hem lift when moving around. Across the body it feels like a more fitted Microlight Alpine Jacket, which may or may not be a useful reference point given that seemingly everyone owns one these days.

Women's Cirrus Flex Hoody 2.0 Fit  © UKC Gear
Women's Cirrus Flex Hoody 2.0 Fit
© UKC Gear

Women's Cirrus Flex Hoody 2.0 Fit  © UKC Gear
Women's Cirrus Flex Hoody 2.0 Fit
© UKC Gear

Weight and Fill

The Cirrus Flex features Primaloft's Silver Luxe synthetic insulation. After fairly extensive research it's hard to say exactly what this means, so here's an attempt to describe it in layman's terms:

Primaloft Silver sits just below Primaloft Gold, which is their most premium insulation. Gold tends to be used in flagship technical pieces that require the utmost warmth, but it comes at a cost. Silver seeks to compromise in this respect, as it still provides good warmth to weight - it's just that it doesn't provide quite as much as Gold. In the case of the Cirrus, Gold would realistically be too warm, so the inclusion of Silver is spot on as far as performance is concerned.

The 'Luxe' element refers to the fact that this particular type of Primaloft is a little different to your average, being more down-like in both its look and its feel. In practise, this is pretty hard to notice, but having had a look through the figures the basic gist is that it's a bit heavier and a bit warmer. One of the added benefits of Luxe, aside from its performance, is that it's made from 100% recycled materials.

Whilst the Primaloft provides the warmth, it's the Thermic stretch fleece panels across the side that arguably make the Cirrus Flex what it is, as it's those that let in that little bit of air, which should (at least in theory) help to regulate your temperature. Without this it would essentially be a belay jacket, but its inclusion is fundamentally what makes it a more active piece.

Men's Jacket - 385g Medium

Women's Hoody - 422g Size 12


Both the Men's and Women's Cirrus Flex 2.0 feature a Pertex Quantum 20D polyamide ripstop outer and a 20D recycled Atmos polyamide ripstop inner. The outer in particular is at the lighter end of the spectrum, but does bear up impressively well considering. Both the men's and the women's have been used whilst climbing on a variety of rock types - some rough, some smooth - and neither have ripped, although it's fair to say that you'd want to be careful. 

Rab's move towards more sustainable fabrics and fills is notable across the board, but no more so than within the Cirrus, where virtually everything is recycled. If this weren't enough, it also features a fluorocarbon free DWR, which adds to its environmental credentials.

Within the venting Rab have used a thermic stretch fleece, which features a firm feeling face fabric with a microgrid backer.

  • Fabric Outer - Pertex Quantum 20D recycled polyamide ripstop/38gsm/ fluorocarbon free DWR
  • Lining - 20D recycled Atmos polyamide ripstop/ 41gsm with Thermic stretch fleece/ 215 gsm/ 94% polyester 6% elastane

It's a nice, simple low-profile hood  © UKC Gear
It's a nice, simple low-profile hood
© UKC Gear

With a snug fit around the face  © UKC Gear
With a snug fit around the face
© UKC Gear


Men's and Women's (shared features) The Cirrux Flex 2.0 Jacket is pretty stripped-back in its design, so most of the features are quite subtle. The cuffs are elasticated and the waist has an elastic cord, which helps to keep its snug feel. On the inside there are two large, open topped pockets, which act as great buckets for things like gloves and/or climbing shoes. On the outside there's two zipped pockets, one of which doubles as a stuff sack. The Jacket has no hood, which we'll count as a point in its favour given that pretty much every layer these days seems to feature one, often leaving you with more head covering than you know what to do with.

Women's Hoody - The hood, much like the cuffs, is elasticated, which gives it a good, snug seal. The insulation around the top means that it keeps that little bit of extra warmth in, whilst the fleece panelling around the sides provides a good balance between extra insulation and extra airflow. A softbrush fleece panel on the inside also means that when it's fastened up it has a nice gentle feel against your skin.

The fleece panels under the arms provide extra ventilation and breathability   © UKC Gear
The fleece panels under the arms provide extra ventilation and breathability
© UKC Gear

Internal pockets are great for climbing shoes, gloves and a range of other nick-nacks   © UKC Gear
Internal pockets are great for climbing shoes, gloves and a range of other nick-nacks
© UKC Gear


Active insulation isn't for everyone, as some will prefer a belay jacket for their outright warmth, whereas others will prefer a fleece for their outright breathability; however, cynical though we were about the category we both found ourselves wearing the Cirrus Flex 2.0 a lot. Part of this comes down to the excellent and comfortable fit, which just makes the jacket extremely wearable; however, important though fit is it would be a moot point if the jacket didn't do what it was meant to do as far as temperature regulation is concerned. In colder weather it's good on the move, while on warmer days it's good as a 'just in case' piece, which makes it suitable year-round - albeit in quite different ways. 

Rab say:

Worn as either a lightweight outer or warm midlayer, the Cirrus Flex Jacket is incredibly versatile, offering durability, breathability, and freedom of movement.

The Cirrus Flex Jacket is lightly filled with Cirrus™3M Featherless insulation, which balances and regulates temperature so you don't overheat while you're moving or get cold when you stop. Designed for movement, the Thermic™stretch fleece panelling offers excellent flexibility and improved breathability. The Cirrus Flex is made with durable Hyperlite™rip-stop outer and lining fabric, which sheds water and is fast drying. The left pocket doubles as integrated stuff sack so it packs away neatly when you're on the move.

Whether you plan to walk, climb, or scramble to the summit of the mountain, or beyond, the hard working Cirrus Flex Jacket is suitable for long mountain days and year round active use as part of a layering system.

  • Sizes: S-XXL (men) 8-16 (women)
  • Fit: Slim
  • Weight:360g 
  • Outer Fabric: Atmos™:,DWR 80/20,36g/m²,20d/20d,100% nylon
  • Fabric Inner: Thermic™:,215g/m²,94% Polyester 6% elastane
  • Insulation Type: Cirrus™,100g in size L
  • Thermic™ stretch fleece with grid face and brushed back panelling
  • Fleece lined chin guard
  • YKK® VISLON® front zip with internal storm flap
  • 2 YKK® zipped hand pockets. Left pocket doubles as integrated stuff sack
  • 2 Interior drop-in pockets
  • Lycra bound elasticated cuffs
  • Hem drawcord

For more information

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2 Sep, 2021

I've been wearing one since December. Pulling a windproof on over the top when you stop ramps up the insulation effect and gives you an instant belay jacket.

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