The Big Test: Three season sleeping bags reviewed (2019)

During spring, summer and autumn, the right 3-season sleeping bag can help make camping in the mountains an idyllic experience. Here’s our pick of the six best down and synthetic sleeping bags for 2019.


The runners up

Mammut Kompakt MTI 3-Season (Women) £159 

Tester: Anna Humphries

  • Lower comfort limit -10°C

  • Insulation Ajungilak MTI Pro polyester 

  • Size 205x80cm (Regular and Short available)

  • Men’s equivalent Kompakt MTI 3-Season (Regular, Large and Wide available) 

  • Packed size 21 x 30cmn 

  • Weight 1851g (inc 100g stuffsack)

This well-priced bag is warmer than other 3-season bags, with a temperature rating of -10°C, while others are -4°C, -6°C or -8.5°C. So not surprisingly, it’s also a little heavier and more bulky when in its stuffsack.

Synthetic insulation means it is less compact but does feel warm instantly, which was a welcome benefit over the down bag I tried, which took more time to become cosy.

The hood, shoulder baffle and zip are all well designed, and there are two sizes each for the women and men’s versions. The women’s option has the extra benefit of a fleece-lined foot area and a bigger hood.

So, what’s not to like? For me this bag’s pink colour with a green zip is a real turn-off. It also lacks the stretchy seams of other higher-priced bags, and is heavy, but of course it is warmer too. Oddly the stuffsack colour is a nice red and black, which doesn’t match the bag but at least the pinkness is hidden when the bag is packed inside!


Price, warmth, fleecy foot in women’s option, two sizes each for men and for women


Weight and packed size, no stretch baffles, pink colour for women’s version 


Vaude Santis 800 SYN £250

Tester: Graham Thompson

  • Lower comfort limit -4°C

  • Insulation Pinnero Mantle 100% recycled polyester

  • Size 220x80cm (one size)

  • Women’s equivalent n/a

  • Packed size 22x28cm

  • Weight 1292g (inc 75g stuffsack)

Like many Vaude products it’s the environmental benefits that shine through with this bag, as it’s made with 100% recycled polyester insulation and its water- repellent finish doesn’t use harmful fluorocarbons (PFC).

Stretch fibres are used in the knee area to allow more comfort, and the shoulder width and length are bigger than some. There’s also a unique additional side zipped arm hole, so you can be inside the bag with both arms out (one arm out via normal side zip, the other through the arm hole).

The weight and packed size are good although, of course, a down bag is even lighter. But also note this is rated as -4°C comfort limit, while other bags here are rated as -6°C comfort limit, so this isn’t quite as warm as the others. There are no extra size or women’s options here either, and the price tag is less friendly than this bag’s impressive environmental benefits.


Environmental benefits, zipped arm opening, stretch panels in knee area, reasonable weight and packed size for a synthetic bag


Price is relatively high compared to other synthetic bags, slightly lower temperature rating, no extra size options or women’s option


Thermarest Hyperion 20F/-6C £400-£420 

Tester: Tim Butcher

  • Lower comfort limit -6°C

  • Insulation Nikwax Hydrophobic 900 fill power goose down

  • Size 216x74cm (Long, Small and Regular available)

  • Women’s equivalent n/a

  • Packed size 16x20cm

  • Weight 688g (inc 50g stuffsack)

New for 2019, this bag is exceptionally lightweight and compact when compressed into its stuffsack. It still carries a temperature rating of -6°C and the weight-saving comes from a numbers of areas. Firstly it uses top quality 900 fill down, so you just need less of it to stay warm, and the shell fabric is very thin 10 denier ripstop nylon.

The side zip only extends to the hip, rather than the foot or calf area, and the zip itself is a lighter-weight design that seems to snag a little easier than others, and tends to open on its own if I didn’t secure the press stud at the top of the zip. There is no shoulder baffle either.

Finally you don’t get the stretch baffles of other sleeping bags. It comes with a pair of thin webbing straps that can be wrapped around a Thermarest sleeping mat for ‘optimal efficiency’, but I didn’t find this of much benefit and felt if I turned over too roughly I may have ripped out the straps.


Weight and packed size. Attachment webbing to sleeping mat may be of benefit to some, but I wasn’t convinced as I tend to sleep on my side and move around too much


Price, short side zip, no shoulder baffle, no stretch in bag size, no women’s specific design



The top three

Deuter Exosphere -6° £170 

Tester: Graham Thompson

Is this synthetic insulated bag so good, there’s no need to spend extra on down insulation?

  • Lower comfort limit -6°C

  • Insulation Thermo Proloft synthetic 

  • Size (Length x shoulder width) 205x68cm (Regular and Large available) 

  • Women’s equivalentDeuter Exosphere -6° SL (one size)

  • Packed size 20x23cm

  • Weight 1319g (inc 88g stuffsack)

It’s good

This sleeping bag uses synthetic insulation, so is available at a much lower price than an equivalent down insulated bag. But the weight, packed size and temperature rating are exceptionally impressive, even compared to down-filled bags.

Elasticated construction allows the whole bag to expand in width by 25%. The elastication also holds the insulation closer to the body, resulting in increased efficiency as there are less cold air pockets, so the bag warms up faster and needs less insulation.

In addition the foot and head have been treated to keep moisture at bay, such as when condensation gathers in a tent. You also get a shoulder baffle, a great hood and a side zip with a good anti-snag design.

I found this bag outstandingly comfortable and warm, and perfect for camping without the cost of a down bag. What’s even better is it comes in both regular and large sizes, as well as a women’s option, and as it is stretchy this bag should fit a wider range of people than most bags.

The compression sack has four webbing buckles to crush the contents, making it easy to create a good packed size.


This bag is rated as -6°C comfort, but a similar weight down bag is rated as -8.5°C. And if you have the cash, a top quality -6°C rated down bag is just 866g, so down is going to be lighter if you compare temperature ratings carefully.

If you’re really picky then this bag could be lighter, with a skimpier stuffsack that vacuum- packs the bag more efficiently. Some grams could also be shaved off by using thinner shell materials, while you could strip out the shoulder baffle and dryzones to save cash too.

There is a chance you may not like the stretchy, body-hugging design. I love it, but some people may want the more spacious feel of a wider bag that doesn’t hug you as closely as this. Finally, some other synthetic bags use more recycled content.


An excellent synthetic-insulated bag that would suit the needs of most backpackers and mountain campers. But pay more and you can have a lighter bag, and if you can live with less features you can pay less or reduce weight.

  • Features 4/5

  • Fit 5/5

  • Comfort 5/5

  • In use 4/5

  • Value for money 5/5



Rab Ascent 700 (Women’s) £260 

Tester: Anna Humphries

This mid-priced down bag offers lots of benefits over synthetic, but is it worth the cash?

  • Lower comfort limit -8.5°C

  • Insulation Nikwax Hydrophobic 650 fill power European duck down

  • Size 205x70cm (one size, women’s)n 

  • Men’s equivalent Rab Ascent 700 (Regular and Extra Long available)

  • Packed size 24x18cm

  • Weight 1325g (inc 66g stuffsack)

It’s good

This is relatively well-priced for a down insulated bag. It uses 650 fill power down (rather than 800 fill power down) to reduce costs, but still has a very reasonable packed size and weight. It also gives you a few extra degrees of warmth compared to some bags, which makes it more suitable for women, who on average feel the cold more than men.

This spacious bag had plenty of room for my hips and legs without feeling tight when I turned over. The side zip extends a good way down to the foot for venting, and there’s also a shoulder baffle to trap air inside.

Hydrophobic down (certified by the Responsible Down Standard to safeguard bird welfare) is used to improve the performance a little more, and is treated with Nikwax to resist moisture. I found the bag did take a little longer to warm up than the synthetic option, but once warm I was extremely cosy and comfortable.

The stuffsack is particularly good, as it allowed me to very easily vacuum-pack the bag down to a very small size.


It is heavier than a bag using down insulation with higher fill power, but of course that is why its price is more competitive. This bag is only available in one size for women too, so if you’re a tall woman you may find you need to look at the longer men’s version.

Some bags have stretch linings to make them even more comfortable and efficient, but that isn’t on offer here. As with any down insulated bag, if it does get damp then its performance drops off rapidly compared to a synthetic bag, although at least here we do have Nikwax-treated down, so this is less of an issue. Of course, while the price is good for a down-insulated bag, if you find the performance of a synthetic bag acceptable you can save a lot of cash by choosing synthetic insulation instead of opting for feathers.


Mid-priced down insulated bag that compares well to costlier down bags. It has most of the key features many mountain campers will need, but pay more and you get a lighter bag, while synthetic options save money.

  • Features 4/5

  • Fit 5/5

  • Comfort 5/5

  • In use 4/5

  • Value for money 4/5


Mountain Equipment Firelite £440

Tester: Tim Butcher

A top-quality down insulated bag with all the features you need, but does it justify the outlay?

  • Lower comfort limit -6°C

  • Insulation 800 fill power Russian goose down 

  • Size 215x65cm (Regular and Long available)

  • Women’s equivalent n/a

  • Packed size 21 x 21cm (size Long)

  • Weight 866g (Long, inc 59g stuffsack)

It's Good 

Designed for ultra- light backpacking and high mountain use, this bag certainly meets its brief. At just 866g and a tiny packed size, this was a doddle to pack into my rucksack and it left plenty of space for other camping equipment.

The bag comes in two sizes, and I tested the Long version given my 198cm height. The width is closer fitting than other bags, but this bag features stretch baffles, so it can expand with your body, but also more loft space is created for the insulation when the lining hugs your body, thereby keeping you warmer.

The insulation is a top-quality down, and the shell material is extremely thin and lightweight. You also get an easy-to-adjust hood and the side zip has a good design that didn’t snag easily. A neck baffle helps prevent warm air from escaping if the hood is not fully tightened. Together this all adds up to a very comfortable bag that was slightly tight across the thigh area but otherwise unrestrictive and warm.

Insulation comes from an audited supply chain called the Down Codex, to ensure welfare standards and quality are high.


To make the bag match my height, sections have been added at the foot, which did mean the side zip doesn’t extend as close to the foot as other bags. So you might get overly warm feet. The bag is narrower than others too, and while it isn’t generally restrictive, a little more thigh space would have been beneficial.

Any bag with down insulation needs to be kept dry, as the insulation will not trap warm air very effectively if it gets damp, so more care is needed here to keep the bag dry compared to a synthetic insulation bag.

This is pretty much a no- compromises bag, and the result is a hefty price-tag that may cause you to, ahem, lose sleep. But for regular backpacking when all- round performance is your need then this is an acceptable price when compared to other options.


Top-quality backpacking bag if you want optimum performance and are prepared to stretch your budget. But the price is quite eye-watering, and synthetic bags perform better if damp.

  • Features 5/5

  • Fit 5/5

  • Comfort 5/5

  • In use 5/5

  • Value for money 3/5



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Marmot Plasma 30 (2013)

The Marmot Plasma 30 has a very hefty price tag, but this is nevertheless an outstanding sleeping bag that pulls off something rare: it actually seems better than Marmot says it is. In comparison to the Rab Infinity 300 – with which it shares a similar InsoTect insulation system and Pertex outer – it manages a higher fill power of goose down, includes little touches like popper closures on the neck baffle and zip ties, yet manages to weigh less than its rival. This is impressive in itself, but the surprises don’t stop there. The Marmot Plasma 30 feels a lot warmer than it suggests; the quoted comfort limit figure is -1 deg C (the Rab’s is -2 deg C) but the Marmot bag feels instantly warmer when used side by side with the Infinity. This could be due to the higher fill power or simply a better fit due to my body shape, but the high loft of the bag and the snugger fit overall means I personally would select this one for a slightly colder night out. Either way, there really isn’t much in it – and while this is arguably the better bag, for this reason that price is a big turn-off.  


Weight (with stuffsack) 644g (665g)
Size 215x76cm
Packed size 35x17cm
Outer fabric Pertex Quantum with DWR
Inner fabric Pertex Quantum
Insulation 900+ fill goose down
Construction InsoTect vertical baffle
Lower comfort limit -1 deg C
Extreme temp rating -14.4 deg C



The Marmot Plasma 30 is an excellent bag – arguably the best here – though not sufficiently so to justify that price tag over near competitors.

Review by Simon Ingram
First published in Trail magazine August 2013

Sea to Summit Traverse XTII 2011

Natural down remains the most efficient insulator for sleeping bags, but it has to be kept dry to retain its outstanding performance. While waterproof shell fabrics can be used to protect the down, these can cause condensation inside the bag, which itself can dampen the down and in turn reduce performance.
Sea to Summit’s new range of down sleeping bags use a combination of the very best down coupled with the very best shell materials. The down boasts a 850+ fill power, which basically means it can fluff up exceptionally well, and the more it fluffs up, the more air it can trap and the warmer it is. Hence the best down leads to the lightest sleeping bags as you simply need less of it.
But having great-quality down is no good if it gets damp. Sea to Summit solves this problem by using 3D NanoShell on the outside of the bag. This fabric is water-resistant and breathable to keep the worst of the water away from the down. But the important element of this shell material is the polyester 3D Barrier, which sits on the underside of the fabric and holds any condensation away from the down while it evaporates through the NanoShell face fabric. The result should be a dry and comfortable night’s sleep.
The trouble with all that wonderful technology is that it is all hidden away inside the bag. The feature I liked the most was the impressive anti-snag strip on the zip, which allowed the zip to work effortlessly without jamming.
I also liked the general comfort of the Sea to Summit Traverse XTII, thanks to the great hood design and easy-to-use drawcords. A nice additional feature is that the bag comes with a good compression sack, an oversized mesh storage bag and a cotton sack to protect the bag during laundering (very detailed instructions explain how to wash and care for this very special product!).

Size 200x75x45cm
Outer fabric 3D NanoShell
Inner fabric 20d polyester
Construction differential cut shell with offset internal baffles
Insulation 95% European goose down, 850+ fill power
Minimum comfort rating -11 deg C
Packed size 22x34cm in stuffsack; 22x22cm compressed
Weight 1210g bag; 1395g including stuffsack
Made in China
Stockist details tel. (0116) 234 4600;

The Sea to Summit Traverse XTII is an outstanding combination of features for those who really want (and can afford) one of the best sleeping bags money can buy.

Marmot Plasma 15 2011

‘Flow Gate’ is Marmot’s name for the system that is the unique selling point of its new sleeping bag. Its purpose is to prevent mass migration of down through the bag, thus avoiding cold spots and keeping the user evenly warm all over.
The construction allows you to manipulate the down along channels within the bag, yet discourages further accidental movement of down while the bag is in use. So far so good; but I found it incredibly difficult to find out how the system works, and ended up having to ring Marmot to ask them. There are no instructions or markings on the bag to explain how to use it, which is a clear oversight. This is a shame, as the Marmot Plasma 15 happens to be rather good, with an impressive performance to weight ratio.
The Flow Gates are positioned about halfway down the bag, with another set a foot or so lower. I finally managed to find them by running two fingers down the inside of the bag between the stitch lines. They feel a bit like a piece of material with a round hole in the middle. Once located, the idea is to massage the down through the holes, along the length of the baffle, moving the down through the Flow Gates as required. This means you can add extra insulation where you need it.
Despite the sleeping bag generally being very good at its job, I found the function quite a hassle. It’s not something I’d fancy attempting at night when camping and waking up due to the cold. But it could be useful if you just wanted to tweak the down distribution once, for example if you tend to get chilly feet. So, while Flow Gate clearly has some useful applications, it doesn’t offer the ideal solution to the problem of cold spots.
The Marmot Plasma 15 itself is super-light and beautifully comfortable. The price isn’t something to be taken lightly, but it’s hard to find a similar specification sleeping bag much cheaper.

Size 183x75x55cm regular (long version also available)
Outer fabric Pertex Quantum with DWR
Inner fabric Pertex Quantum with DWR
Construction vertical baffles
Insulation 500g of 900+ fill power goose down
Minimum comfort temperature rating -7.8 deg C
Packed size 19x32cm; 19x18cm compressed
Weight 856g (bag only); 880g (with stuffsack)
Made in China
Stockist details – tel. (015395) 63616;

The weight of the Marmot Plasma 15  is outstanding, making it an ideal sleeping bag for 3-season backpacking; but the Flow Gate function needs a clearer explanation for users.

Review by Graham Thompson
First published in Trail magazine Spring 2011

The North Face Solar Flare 2009

Designed as an expedition sleeping bag for high-altitude trips, the The North Face Solar Flare boasts an extremely warm temperature rating of -18 deg C. More importantly though it also uses trapezoidal baffles for the ultimate in construction methods, so that cold spots are reduced to a minimum. The shell is made from waterproof and breathable Hyvent fabric to help keep the down dry.


The Solar Flare boasts a set of unique features to make it comfortable even in the worst of winter weather. The bag has synthetic panels of Climashield Prism insulation within compression zones down the back of the bag, so that these areas are not compressed, resulting in an improvement in warmth while improving efficiency by 13 per cent according to the manufacturer. The body of the bag has trapezoidal baffles, box wall baffles on the sides and there are seven baffles in the hood, which all adds up to controlled distribution of that precious down insulation. The foot box is enlarged, with a taper for a better fit, and there is a huge plug of down in the foot too for extra warmth around your toes. The side zip extends almost to the foot and is protected by a massive and well-filled draught collar to prevent cold spots. Also there is a shoulder baffle too, which is again wide and well stuffed with down. All that is packed into a waterproof shell so that the insulation’s efficiency is not compromised by dampness.


On the hill
The bag comes with a compression stuffsack that allows its relatively high bulk to be easily cranked down. The first thing I noticed when using this high on Glaramara was the foot shape, as my size 11 feet did not squash down the insulation. As this is a very warm bag, I was soon opening the zip for more air. It was noticeable how easily it slipped up and down without snagging and jamming, which is just what you want. It would be nice if that zip extended a little further to the foot, as I found my feet cooking at times, however usually your feet will need all the insulation they can get in the depths of winter. I particular liked the hood and shoulder baffle, which fitted well and were easy to adjust thanks to three different cord sizes that I could adjust in the dark. The shell is made of waterproof fabric, but the seams are not taped, and I found the down did get wet from a puddle of condensation in my tent.   


Size 230x80x50cm long (medium also available)
Fill weight 1040g
Fill power 800 (US)
Comfort temperature rating -18 deg C
Packed size 32x27cm compressed
Weight of bag 1915g
Made in China
Stores in the UK 2
Stockist details tel. (01539) 738882;


Verdict: The North Face’s Solar Flare is a very warm sleeping bag that is ideal for the coldest of temperatures but price, weight and lack of waterproofness are drawbacks.