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Setting the milestone for modern alpinism, the Sigma from Mountain Equipment is obsessive in it's construction and one of the only choices for fast and light mountaineering goals. 

Setting the milestone for modern alpinism, the Sigma from Mountain Equipment is obsessive in it's construction and one of the only choices for fast and light mountaineering goals. 

Mountain Equipment

Mountain Equipment Womens Sigma Jacket Cosmos

£170.00  £340.00  50% off
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Estimated Delivery & Collection Dates

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The dates we provide are based on indications given by our suppliers. Whenever we get updated information from our suppliers we will endeavour to update the Estimated Delivery & Collection Dates provided on product pages.

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Mountain Equipment Womens Sigma Jacket Cosmos Information

Season : Sale

Brand : Mountain Equipment

Code : 001852-01286-

The Mountain Equipment Sigma Jacket is pretty much the perfect lightweight down jacket for fast and light mountaineering adventures. Made with an uncompromising design to ensure maximum insulation, minimal weight and an outstanding pack-size, it excels in the world of modern alpinism and big mountain expeditions. 

As well as providing maximum insulation, the Sigma is windproof and highly water resistant, so you can use it as a standalone jacket in our typically cold and wet UK conditions, or layer it underneath a shell jacket in more extreme environments. It also works superbly as a belay jacket to chuck over the top of all your layers to provide warmth on those exposed belays, or when stopping for lunch on winter outings. How you wear it will depend on what you’re doing, how much effort you’re putting in and of course what the weather conditions are.

What is the Sigma Down Jacket made from?

The outer of the Sigma Down Jacket is constructed with Mountain Equipment’s own Drilite Loft fabric. Drilite Loft is an extremely tough, breathable and water-resistant Nylon fabric with a microporous Polyurethane coating that provides a hydrostatic head of 1500mm to keep the insulation dry in hostile environments.  It has also been treated with a Durable Water Repellent (DWR) to help water bead up and run off, but even though the fabric is incredibly weather resistant and windproof, it is not 100% waterproof, so always carry a shell jacket, because it will rain!

Mountain Equipment have also used the Drilite Loft fabric to line the inner hem, hood lining and pocket openings, as these are areas that are particularly prone to getting wet. The rest of the inner jacket is lined with an un-coated nylon to maximise breathability and softness next to the skin.

The stuff that’s keeping you warm inside this lovely jacket is M.E’s very best Eastern European goose down with an 800-fill power. What’s fill power? Well, for those who don’t know, it’s an internationally recognised measurement of how well down will “loft”. Loft describes how “fluffy” the insulation is, the “fluffier” down is the more space it can occupy and the more warm air it can trap in all those fine filaments. Down simply doesn’t work when compressed. The number used in Fill Power describes the amount of space one ounce of down will occupy in cubic inches when allowed to reach its maximum loft. So, in the case of the Mountain Equipment Sigma Jacket, one ounce of down will loft up to fill 800 cubic inches, or to put that in perspective, it’s equivalent to about 13 litres, or the same as a Large Exped Fold Dry-Bag.

What makes Mountain Equipment's down so special is their Down Codex programme. Most companies are now taking steps to make sure their down is coming from ethical sources, but Mountain Equipment are taking the whole process to another level. The waterfowl (geese and ducks) are all by-products of the food and meat industry, every supplier wishing to work with Mountain Equipment must accept the terms of their Down Codex and allow a full audit of all parts of the supply chain - that means everything from farm to factory. On top of all of that, you can even trace your down on their website right back to the source using a unique 12-digit code printed on the label inside every Mountain Equipment down product. In fact, Mountain Equipment are so proud of how ethical their down is, they’ve sewn a label to the inside telling you all about it, and there’s even a leaflet in the pocket with the full story.

All that lovely, ethical down is kept in place in stitch-through baffles to keep it close to your body to maximise performance. In fact, each and every baffle has been optimised for down distribution and fill weight to maximise performance.

The use, throughout the Sigma, of technical, lightweight fabrics and high quality down keep the overall weight (size Medium) to around 570g.

What are the main features?

The hood on the Sigma is a key feature for us at Trekitt, especially me, I love a good hood! M.E have used their Half Dome HC hood design, which basically means that it’ll work well over a helmet and also over your bare head. The trick to this exceptional fit is M.E’s EXL lining, borrowed from their sleeping bag construction, EXL linings have elasticated stitching that allows the hood to sit close to your head, or stretch to fit over a hat or helmet. The massive benefit is that the insulation is always kept close to your head to maximise warmth and comfort. You also get a stiffened peak to stop it flopping down over your eyes and side draw cords with captivated ends to stop them whipping you in the face when it gets windy. The hood also gets a full Drilite fabric lining to stop sweat and moisture from penetrating the down insulation.

The main zip is a reliable two-way YKK moulded version to reduce ice build-up and it is backed up by an offset insulated internal baffle to keep out the drafts.

Storage wise, you get two YKK moulded zipped hand pockets with a panel of Drilite Loft fabric at the entrance to help stop water wicking its way into the pockets. There’s also a zipped internal mesh pocket to keep valuables safe and warm.

The sleeves are finished off with a part elasticated and part Velcro adjusters to tightly seal out the cold over bare wrists or bulky gloves. At the hem you get dual tether hem drawcords, these allow you to tailor the fit and they avoid snagging on ice axes or poles as there’s no loop. The hem also gets a Drilite fabric lining to stop water run-off from wicking up the lining and penetrating the down insulation.

How does the Sigma Down Jacket Fit?

As a technical insulating jacket, it’s designed to fit closely to maximise the insulation. The last thing you want is a big baggy jacket as you’ll waste energy warming up all that dead air space, and conversely you don’t want it too tight either as that’ll hinder the downs ability to fully loft. 

The first thing you notice when you put the Sigma on is that it has a close fit around the hips and trunk, with plenty of room in the chest and shoulders to allow full freedom of movement and reach. I’m 5’1”, weigh around 50kg and I’m wearing a size women’s XS, and it fits perfectly.  However, if you were looking to buy this as an everyday “coat” you might struggle to get it over bulkier clothing and it’d worth considering a more regular fitting alternative, such as the M.E Lightline, or Arcteryx Thorium AR

Where does the Sigma Down Jacket fit in the layering system?

The Sigma Down Jacket works best as an extremely light-weight, breathable outer jacket when you’re out in the mountains in typical UK damp and freezing conditions. Because it is highly packable it can be carried in your pack for use as an insulating over-layer on belays or food stops, or, in extreme conditions it works under a shell jacket as an efficient and very warm insulating layer. Basically, it's super versatile!

Layering is not a precise science and there is no one perfect system that will suit every person, situation or the weather conditions. Some of us feel the cold, others, like me, get hot very quickly, but for more advice on using layers please check our YouTube video


So that’s it, the Mountain Equipment Sigma Jacket, an incredibly lightweight, comfortable, technical and versatile performer for all mountain adventures; it fits superbly and is beautifully made thanks to Mountain Equipment’s 50-year experience in making gear for the most inhospitable places on the planet.

  • Lightweight
  • Packable
  • Drilite loft 30D outer
  • Windproof and highly water resistant
  • 210g (Size 12) of Goose Down with a MINIMUM content of 90/10 800 fill power
  • Stitched-through baffle construction throughout
  • Optimised down distribution and fill weights using a baffle-by-baffle approach
  • Half Dome HC hood with EXL lining
  • 2-way YKK moulded centre front zip with an offset insulated rear baffle
  • 2 zipped hand warmer pockets with moulded zips
  • Drilite Loft 30D hem, pocket and hood lining
  • Adjustable cuffs and dual tether hemcord

How to wash your down products

Having spent years talking to people about down products, whether that’s a jacket, sleeping bag or even a pair of slippers, very few have had the confidence to go ahead and wash the product on their own, especially when they have just spent an arm and a leg on it. This small guide is here to explain that it’s not as daunting and utterly terrifying as it first appears.

Step one: Before you even get near that washing machine, wipe off any excess mud or dirt that may be lingering on the surface of the jacket, as this will clog up the washing machine, eventually rendering it useless.

We recommend the use of Nikwax Down Wash Direct for down products as it’s one hundred percent environmentally friendly and will wash and re-proof the garment without the use of bleach or any other nasty chemicals. What household washing agents can (and often do) is remove the water repellent coating on the fabric of the jacket, whilst also damaging the delicate array of feathers inside.

Step two: We’ll assume in this instance that you’ve been washing other products prior to your down jacket and have used a bleach based detergent. Therefore it’s a good idea to run the washing machine for half an hour or so without anything inside to rinse it clean before adding the Nikwax or putting the jacket in. Also, don’t forget to remove the detergent drawer to give it a wash inside, outside and behind, as detergent can clog up and still enter the washing machine if not cleaned out thoroughly. This ensures that any remnants of detergent are removed and that the Nikwax products will work effectively.

Step three: Set the washing machine to a cold wash (check the garments care label, most tend to be around 30°C) and as delicate as possible. Most washing machines have a “wool” cycle which is ideal.

Step four: If using Nikwax Down Wash Direct, place 100ml in either the tray or directly into the washing machine inside a small pot/ball. If you choose to use another washing product, place the appropriate amount in the machine in the same way.

Step five: Set the washing machine to run on a slow cycle, allowing plenty of time for the jacket to soak up the cleaning/re-proofing product. Most washing machines will have a pre-set time for different washing cycles.

When the cycle has finished be prepared for a shock, your precious bit of kit will come out looking like a soggy ball of material. But don’t worry, you haven’t ruined it, it’s just that all that fluffy down insulation has become water logged and has clumped together. The trick is to now get all that down nice and dry to reinstate its superb insulating properties. Simply hanging it up in a warm place will not work that well. It will take days to properly dry and you will have to constantly break up the clumps to get it thoroughly dry. The best way is to use a tumble dryer; either a domestic one for smaller items or a commercial drier for sleeping bags.

Step six: Pop the garment into the dryer and make sure to select a low heat; a high heat runs the risk of melting seams and fabrics within the garment. It sounds weird, but shove a few tennis balls into the drier with the garment; the tennis balls will bounce around and help to break up the clumps of down. Every 20 minutes, pull the jacket out of the dryer and lie the jacket down on a table. Run your hands over the jacket until you find a 'clump' or ball of down; tease apart this down clump and spread it evenly into the baffle. Once you're confident you've pulled apart every clump to the best of your ability, stick it back in for another 20 minutes. Keep repeating this until there are no more clumps left. 

Step seven: When the cycle has finished and you are sure that you have got the garment as dry as possible, hang it up in a warm dry place, an airing cupboard is ideal, for 24 hours. This drives out the last of any dampness and allows the down to loft fully. Take it out and give it a good shake and, hey presto, it’ll be as good as new.


Technical Information

Weight: 570g / 20.1oz

Down: 201g (Size 12) of Goose Down with a MINIMUM content of 90/10 800 fill power

Fabric: 30D / 30D - 53g / 1.9oz.

Content: 100% Polymide outer/inner

Sizing Information

Click here for the manufactures size charts.

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