Rab Alpha Flux Jacket Review

'Active insulation' is all the rage this season. Put simply, this is fluffy stuff developed primarily for breathability and moisture management, making it comfortably unclammy when worn on the move and yet still warm-ish (within reason) when you're stationary. Rab's new Alpha Flux Jacket is a perfect example.

Hot sun, cold shade, nippy breeze and hard graft - tricky to dress right, but the Alpha Flux works well, 168 kb
Hot sun, cold shade, nippy breeze and hard graft - tricky to dress right, but the Alpha Flux works well
© Dan Bailey

In look and feel it's like a softshell. Or is it better described as an ultra light synthetic insulated jacket, but with the lining fabric removed to expose the insulation on the inside? No, wait, I know, it's a stripped-back 21st Century take on the Buffalo jacket principle, with a pile-like lining and a smooth outer face... OK, you get the idea: The Alpha Flux defies neat categorisation.

Never mind how you'd define it - what's it for? I've found it functions equally well whether treated as a breathable midlayer under a shell, or as a featherweight stand-alone outer in moderate weather. I'd say it's only really a 'jacket' in the sense of having a full-length zip; but 'highly technical cardigan' doesn't have quite the same ring. In essence the Alpha Flux performs a similar role to a fancy micro fleece, but with a bit of added weather performance when worn on top. It's a real hybrid then, and this makes it a very versatile wee beastie.

High collar protects neck and chin, 162 kb
High collar protects neck and chin
© Pegs Bailey

I've worn it cragging; wild camping; hillwalking through autumn, winter and into spring; and as part of a layering system when winter climbing. Since it's also light and packable enough for carrying just-in-case in summer, I'm struggling to think of an occasion when the Alpha Flux wouldn't be useful.


The knit is so open it's practically transparent. Left: Alpha Direct; Right: Thermic-lux stretch fleece, 211 kb
The knit is so open it's practically transparent. Left: Alpha Direct; Right: Thermic-lux stretch fleece
© UKC/UKH Gear

Key to its comfort on the move is Rab's use of Polartec's Alpha Direct insulation. The original Alpha is designed to be used as an insulating fill between two layers of face fabric, but with the Direct version Polartec have removed the inner fabric to expose the fluffy stuff. This takes the form of a very light, open weave pile that offers plenty of warmth for its minimal weight (only 95g/m2 ). To keep you warm, air is held in the spaces between each tuft of insulation, yet the low density of the knit lets air and moisture move freely through the garment. Impressively quick drying and breathable, the insulation doesn't hold onto moisture when you're busy working up a sweat, making the Alpha Flux particularly comfortable and non-clammy for high output activities, be that steaming up a winter gully or lugging a heavy pack uphill. That furry inner face feels lovely and luxurious, and the lack of a lining layer means that the insulation can do the best possible job of wicking.

This lack of lining also helps keep the weight down - I make it just 367g (size L), which is not going to break the bank at any time of year.

Polartec Alpha Direct - ideal insulation on the go in spring or autumn hill weather, 203 kb
Polartec Alpha Direct - ideal insulation on the go in spring or autumn hill weather
© Pegs Bailey

On the outside is a very lightweight face fabric. Suitably air permeable to help make the most of breathability and moisture transport, you can feel even a light breeze through it and yet it still manages to take some of the edge off the wind. Thin and extremely soft to the touch, without seeming unduly delicate, this has loads of stretch for freedom of movement.

To further boost the non-sweaty feel Rab have zoned the Alpha Direct insulation only where it's most needed - on the front and back of the body, down the top of the sleeves and on the sides of the hood. Elsewhere - along the underside of the arms, down the sides of the body and most of the hood - it's a very thin and extremely stretchy 'fleece' fabric with a soft brushed inner. This feels practically as light as a base layer, and has the breathability to match.

Working up a sweat without getting too clammy, thanks to the Alpha Direct and the thin side panels, 166 kb
Working up a sweat without getting too clammy, thanks to the Alpha Direct and the thin side panels
© Dan Bailey


Rab's description of the cut as 'trim' is spot on; the Alpha Flux has a close, athletic fit, so while it layers neatly over a baselayer you're not going to be donning this, belay jacket style, over multiple other garments. Combined with the stretchy fabrics, the tailoring offers complete freedom of movement for climbing etc; this is active insulation, with emphasis on the 'active'. It is medium-long in the body, with a slightly lower rear for partial bum coverage, and stays neatly in place under a harness or rucksack hipbelt. The sleeves are long, so the wrist stays covered even when you raise your arms; thumb loops help in this regard too, though I find the openings rather small for my thumbs (no big deal - personally I'm not loopy for loops anyway).

The hood has a good shape, but no volume adjustment or stiffened brim, 156 kb
The hood has a good shape, but no volume adjustment or stiffened brim
© Dan Bailey

The stretchy hood offers a nice close fit without limiting movement, and though it won't fit over a helmet it certainly works well when worn underneath one. There's no stiffened brim or any attempt at volume adjustment, and while that might be a disadvantage in a beefier duvet style jacket this simplicity is appropriate to the stripped-back character of the Alpha Flux. The hood is sufficient for a bit of a warmth boost at the belay, or keeping the wind off your ears on a summit stop; if conditions are really cold and wild however, then the chances are you'll be wearing the Alpha Flux as a midlayer and retreating into the more substantial hood of your shell. With the hood down, the collar still zips up nice and high to give plenty of neck protection.


Two good-sized hand pockets , 159 kb
Two good-sized hand pockets
© Dan Bailey

On a top like this you don't want a lot of pockets or other clutter. The Alpha Flux has just two decent-sized zipped hand pockets, mesh-lined in order to function as vents should the need arise. These are largely accessible when you're wearing a harness or rucksack hipbelt, but not fully so, and ideally could do with being positioned a fraction higher. The full-length zip, a medium-gauge YKK, is backed with a little draught excluding strip, and comes with a glove-friendly pull tag. There's no volume adjustment at the hem. I don't think one is needed, but I do wonder if a little bit of elastication around the bottom might have been a worthwhile addition: as it is, the hem hangs loose and can tend to lift in a strong wind.


Quick drying, ultra light and highly breathable, the Alpha Flux exemplifies the new breed of 'active insulation'. The open knit of the fabric offers superb air flow and moisture management, so when it comes to insulation you can genuinely wear on the move this jacket is up there with the best. Whether treated as a cold weather midlayer or a skimpy stand-alone outer, it is a versatile piece of clothing with year-round appeal. In winter however you'll need additional warm layers on top.

Rab say:

The new Alpha Flux Jacket from Rab is an incredibly versatile jacket that can be used in a variety of roles across different seasons and activities. Utilizing the new Polartec® Alpha® Direct Insulation, the Alpha Flux keeps your body temperature in balance when moving fast and working hard in the mountains. This unique insulation removes the need for a lining fabric, dramatically reducing weight and bulk, whilst boosting breathability and drying time.

The Alpha Flux is shelled in a super-soft yet durable woven outer fabric with high levels of air permeability. Paired with Thermic-lux ™ light stretch fleece in strategic areas of the body, the jacket provides exceptional comfort and freedom of movement.

An excellent mid-layer for windy, cold conditions and the perfect insulation piece for warmer seasons.

  • Fabric: Polartec® Alpha® 'Direct' 90 insulation
  • Under helmet hood
  • YKK® front zip, internal storm flap, chin guard
  • 2 YKK® zipped hand pockets
  • Stretch fleece panels, cuffs and thumb loops with Polygiene® STAY FRESH™ odour control treatment
  • Fit: Slim
  • Weight: 367g (size L, our weight)
  • Sizes: S – XXL (Men), 8-16 (Women)
  • RRP: £135

Rab Alpha Flux jacket prod shot, 57 kb

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