Gilets may not be the most exciting category of clothing, but they are really versatile, giving you a lightweight insulation boost with less bulk and restriction than a sleeved alternative. Having been without one for some years, I've barely been parted from the Cirrus Flex Vest since it arrived at the start of lockdown. I'm not sure I can think of an occasion, climbing or hillwalking, summer or winter, when it wouldn't be worth considering.

What's it for?

At 254g in a size L the Cirrus Flex is very light, and I think that partly explains why it's so useful. Hillwalking, rock climbing, weight conscious backpacking, queuing outside ASDA... if you can't wear this gilet doing it then it's probably not worth doing. This spring/summer I've been sticking it over the top of whatever else I'm wearing when things get a bit chilly; in winter I'll experiment with using it deeper in the layering system to add a bit more core warmth with minimal bulk. Not having a hood will be helpful when it comes to layering.

If you're not convinced about gilets, a sleeved version is available, the Cirrus Flex Jacket, and there's also one with a hood.

Fit

Though described as slim fitting I'd actually call it pretty roomy, and in my standard size L it's got plenty of space to layer over the top of other clothes, such as a baselayer and thin fleece or softshell. The arm holes are not too close-cut, and there's a bit of stretch here to aid free arm movement. I can climb without the hem lifting at all. Pictures of the women's version look more fitted but the men's seems a little boxy, particularly over the shoulder where it can look a bit odd under rucksack straps. To tighten things up I tried going down to a Medium, but that worked too well, and there's not much point in a skin tight gilet.

The Cirrus Flex is cut long in the body too, sitting well below the waist and covering most of my bum - which of course helps keep the draught out and the heat in. This length is also good for staying tucked under a harness while climbing. With only a mid-height collar you don't get loads of neck coverage, but I think it's appropriate for the sort of garment this is.

Insulation

Lightweight warmth is provided by Rab's 3M Featherless insulation in the front and back of the torso. Advertised as being down-like, this is one of the breed of synthetic fills that first became the rage a few years ago. It's like down insofar as it's quite compressible, but also has a decent amount of loft - and Rab suggest it's equivalent in those terms with 600 fill power down. Of course 600 fill power is only so-so by industry standards, and accordingly the loft, compressibility and warmth for weight of the Cirrus Flex are not on a par with high-end lightweight down duvets. On the other hand this synthetic fill is going to work a bit better if you get damp, and I've found I'm less precious about how carefully I have to treat it.

You get 110g of fill in a size Large. This sounds a fair bit for a sleeveless gilet, but the feel is that of a very thin lightweight insulated jacket, so judge it in these terms. As your main insulated piece the Cirrus Flex Vest is very much a spring/summer weight. I've found it the ideal thing to slip on over a couple of other layers on breezy walks or evening sessions on my local sea cliff. In colder conditions it'd need to be considered a midlayer.

Fabric

To aid breathability and freedom of movement, there are side panels in a light and stretchy fleece fabric. This combination of fleece and core insulation feels spot on for a lightweight gilet like this, and you can work hard without getting too hot and sweaty. Over the front and back of the body, the face fabric is a ripstop polyamide, which feels durable and pretty wind resistant.

Features

Two zipped hand pockets are provided; these are big enough for a pair of gloves, and remain at least partially usable when wearing a harness (not that you'd want to). One of these pockets doubles as a stuff sack, for easier packing or to hang off your harness on multi pitch routes - an excellent feature that I think all lightweight jackets could benefit from. You also get two deep interior drop-in pockets, though I doubt I'll ever use them in this case since this sort of thing seems more important on a winter belay jacket.

The hem drawcord runs only around the rear of the gilet, which is fine, and the elastic tails are directed up inside to avoid the risk of them snagging. A brushed chin guard completes the list of features.

Rab say:

With its featherless insulation and Thermic™ stretch fleece panels, our Cirrus Flex Vest provides core warmth while retaining excellent breathability and ease of movement.

The sleeveless design of the Cirrus Flex Vest eradicates bulk around the shoulder, enabling the full range of movement while keeping your core fully insulated. Designed to deliver an authentic down-like feel, our 3M featherless insulation stays warm while wet, making it ideal for damp British weather or for extended trips where rapid drying is vital. Additional features include an integrated stuff sack, fleece-lined chin guard and a pair of zipped handwarmer pockets, as well as a half-hem drawcord for a fine-tuned fit.

• Weight: 254g size L (our weight)
• Sizes: S-XXL (men) 8-16 (women)
• Cirrus™ powered by 3M featherless insulation (110g in size L)
• Thermic™ stretch fleece with grid face and brushed back panelling
• Atmos™ rip-stop outer and lining fabric
• Fleece lined chin guard
• YKK® VISLON® front zip with insulated baffle
• 2 YKK® zipped hand pockets. Left pocket doubles as integrated stuff sack
• 2 Interior drop-in pockets
• Part lycra-bound armholes
• Half hem drawcord
• Fit: Slim

For more info see rab.equipment