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    The Development of Firestorm: the Birth of the Kryos, Xeros and Exo

    • Product Development

    This winter sees the launch of our new Kryos, Xeros, and Exo jackets, and our new Kryos pants, all developed through rigorous testing both in the lab and the mountains. It’s been a fascinating journey that’s united our product team and pro partners in the pursuit of kit that makes the difference on the most serious modern routes.


    The project started three years ago when Paul Ramsden, an obsessive gear nut – the sort of person who weighs everything in his possession, buys imported handmade ice axes on a hunch that they will work, and ask brands to make stuff to his specification when he can’t find it elsewhere – approached us for a trip that he and Nick Bullock were planning to China. Their objective peak Minya Konka is 7556 metres high, plagued by notoriously bad weather, and would involve at least a week away from base camp. In particular, he feared that the summit ridge’s staggering altitude and exposure would funnel the worst of the weather at them, and he could see them having to climb for long periods in their down jackets, making low bulk and manoeuvrability key, alongside weather resistance, warmth, and of course minimal weight.

    It sounded like a great project. We had already seen Tom Livingstone use his Vega Jacket to 7000 metres on Latok I, but we considered that the absolute limit for the Vega’s design. With its exposed stitch lines it could be compromised in sustained high winds and this was an obvious area for improvement. Nick Bullock has had considerable success using a K7 Jacket to extreme high altitudes, including in his Piolet d’Or winning expedition to Tibet with Paul, but though exceptionally warm it’s not easy to climb harder pitches in. We needed something new.

    Early development

    We drafted a few ideas and decided that weatherproofness was what was needed most of all. That meant covering up stitch lines. This reduces water ingress, prevents snow sticking to the jacket, and greatly reduces the effect of wind blasting through these areas of weakness. Critically we had to do this without appreciably increasing weight. The best approach to covering stitch lines is to use a ‘drop outer’, that is a completely separate layer of fabric over the top of the jacket, almost like covering the jacket in an outer shell. We made a prototype as quickly as we could before field trials began almost immediately. A month long expedition with Paul and Nick was a baptism of fire for the jacket. Though their trip was thwarted by enormous snowfall Paul came back delighted with the prototype:

    At this point, the jacket still didn’t have a name. It was just ‘PR Wad Jacket’ (i.e. Paul Ramsden Wad Jacket, ‘wad’ being Peak District slang for an ‘excellent climber’), and its lighter (‘LW’) sibling that we were planning was ‘PR Wad LW Jacket’. Those names stuck for a long time.

    Baffle design

    With the encouraging feedback from Paul we started refining the design, and this is where we really got to work on the baffles that control the down inside the jacket. The problem is that there’s no such thing as a lightweight box wall jacket that will stand up to sustained bad weather, and there’s no such thing as a lightweight stitch-through jacket that will hack it in serious, sustained cold.

    Simply, baffles hold down in place and allow it to loft fully. If a baffle is too large then down will migrate inside it, creating cold spots but if it’s too constrictive then the down will not provide as much warmth as it should. The amount that down will migrate depends on where the baffle is, with areas like the elbow particularly prone to migration and thus requiring smaller or more controlling baffles than those in more static areas. We optimised the baffle types in the prototypes to try to control the down fill as much as possible whilst making sure key parts of the body such as the torso were kept as warm as possible.

    Traditionally, lightweight and midweight down jackets are constructed using stitch through construction.  This is a relatively simple method that allows the greatest freedom of movement but with the downside that the stitch lines reduce protectiveness and warmth.

    When stitch through baffles are no longer deemed warm enough, we tend to begin using box wall baffles, which are far warmer. However, the stripping that divides the inner and outer fabrics adds considerable weight and the bulk of these baffles greatly reduces the wearer’s freedom of movement.

    A good middle-ground for medium weight jackets is a pleated baffle, extra fabric is incorporated into the baffle to increase its loft and the insulation it provides but stitch lines remain the weak point for heat loss.

    We’ve used a mixture of the different baffle types throughout our new jackets, varying them depending on the warmth required to maximise their relative benefits. This is why if you turn one of our new down jackets inside out you’ll see a bewildering array of different baffles types: they are indicative of our obsessive and performance‑led approach to baffling, each one trying to eke out every iota of warmth from every gram of down.


    The drop outer, the loose fabric outer that covers the baffles, was our secret weapon. It’s not a new idea, it’s one we’ve been using for 50 years, but recent developments in fabric technology have made it a viable one for modern alpine climbing where every gram counts. Gore-Tex Infinium™ fabrics have already been used to great success on our Extreme Expedition series of sleeping bags, and being completely windproof, highly water resistant and very lightweight, we knew they’d be perfect.

    Firestorm allows the advantages of stitch through construction – freedom of movement and low weight – to be harnessed while negating the problems of stitch lines and uneven insulation in stitch through garments. We also wanted to prove that it made a garment warmer. The theory was that it would trap the boundary layer of air between the baffles that is otherwise lost in anything other than completely still conditions.

    Lab testing

    Theories and anecdotes don’t really stand up to scrutiny, so we planned multiple experiments to determine the effect of Firestorm. We spent a long day at -20 °C in Leeds Beckett University’s environmental chamber with two people of very similar heights and weights wearing identical underlayers but switching between different jackets, those with and without Firestorm construction. We covered each person in temperature sensors, used an infrared camera, and crunched through a lot of data. We had our test subjects stand in different positions, remain static for long periods, and stood them in front of a high speed fan to simulate different wind speeds. The anecdotal evidence – that from the test subjects – was unanimous, that Firestorm made a serious difference to how warm they felt. However, the data we’d captured was far from conclusive, and while there were some suggestions that Firestorm made a difference we had nothing concrete. That’s the problem with developing a new technology and a new testing method at the same time: it’s rarely definitive. So we had to do more testing.

    Next we went to the Aitex Textile Research Institute in Spain. We took an existing ISO Standard test and modified it to accommodate such warm products. A thermal manikin, very similar to the one used for assessing the warmth of sleeping bags, was dressed in a climber’s typical clothing, and then each of our test jackets were put on top of these layers. We saw significant differences between how warm each of the garments were. The testing showed that Firestorm construction increased thermal resistance, and that the benefit was greatest when applied to lightweight jackets, with a 20% increase in warmth measured. The thermal performances of midweight jackets were improved by 10%.

    Expedition testing

    As useful as lab testing is, it is no substitute for real life use, and final prototypes of our newly-named Kryos jackets with Firestorm construction were put through their paces by four of our pro partners.

    The feedback was unanimous: that the combinations of low weight, increased warmth, improved protection and the greater manoeuvrability that the Firestorm construction affords were unrivalled. Also, its benefits are most noticed when conditions are at their worst, when wind and weather protection is most important. Before reaching market, the Kryos Jacket had seen more expedition use than most jackets do in years of commercial availability.

    There are six new down products utilising Firestorm construction: 

    Kryos Jacket, Kryos Women’s Jacket

    The Kryos Jacket is the result of over two years of prototyping and development work, with jackets put through their paces by Paul Ramsden in China and Nepal and in Pakistan with Tom Livingstone, Uisdean Hawthorn, and Chantel Astorga. Tom Livingstone’s successful ascent of Kyo Zom was made using a Kryos Jacket.

    The Kryos is exceptionally warm, extremely protective, very lightweight and allows you to climb unencumbered. The unique combination of baffles has been laboured over and the hood is brand new, being more protective and better in extreme cold weather than any hood we have previously developed. In lab tests the Kryos Jacket came out 10% warmer than the Vega Jacket, our classic jacket that has been used to over 7000 metres.

    Kryos Pant 

    The Kryos Pant was developed specifically for Nick Bullock’s and Paul Ramsden’s ground-breaking expedition to Minya Konka in China last year. Two pairs were handmade in the office and the feedback on them was so good (“best insulated legwear I’ve ever worn”) that we have introduced them into the range.

    With an outstanding fit and the Firestorm construction providing unrivalled weather protection, they can be worn all day or carried ‘just in case’. They have a similar weight to many synthetic overpants but are two or three times warmer. Our extensive cold chamber work over the last five years has consistently shown that for a typical mountaineer, adding insulation to your legs is usually the best way to increase your warmth. 

    Xeros Jacket, Xeros Women’s Jacket

    The Xeros Jacket is the younger brother to the Kryos Jacket. The protectiveness of the Firestorm construction and outstanding hood design remain, but the jacket’s weight has been reduced, making this a perfect jacket for everything from lightweight expedition use to ski touring or alpine climbing. Lab testing has shown that the Xeros is a full 20% warmer than an equivalent stitch-through baffle jacket. The weather resistance of this garment also means that environments traditionally reserved for synthetic jackets are now opened up to a down jacket, with the associated warmth, weight and bulk benefits this brings.

    Exo Jacket 

    The Exo Jacket takes much of the Kryos Jacket’s technology, further increases the weight of down and seals the seams (they are fully taped) to make an exceptionally warm and completely weatherproof down jacket. Using a more durable 30D version of Gore-Tex Infinium™ and with a feature set designed for any eventuality, this jacket will stand up to pretty much anything. If you want an absolute bomb shelter that will take any amount of wet, cold, and foul weather then this is that jacket, whether climbing, mountaineering, or skiing. 

    More on Firestorm



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