Sleeping bags for 4 seasons - a modular concept
08 November 2008
Note: Many of these articles are very old, and although the technical information is still relevant the equipment mentioned may not be (for example a Stormy cooker was state of that art in 1995, but not in 2021).
When you ask a climber what type of sleeping bag they would ideally like to buy, they will generally reply that they want an ‘all-round’ bag that will do everything. But in these days of globe-trotting climbers, climbers who do a bit of everything, ‘all-round’ means quite a lot. A climber may want their bag to keep them toasty Scottish winter camping, dosing beside the hire car in Corsica, or stuffed in the bottom of their haul bag is they jam up the Nose, ready for the summit bivy after their one-day ascent. Sounds great doesn’t it, but is it possible? (having such a bag, not climbing the Nose in a day).
Well unless you have the metabolism of a sloth, or live in California, it’s not possible to have one bag that will work as both a true 4 season and true 1 season bag, as a winter bag would leave you boiling in summer, and a summer bag would have left you with chattering teeth in winter (they don’t have seasons in California). The only way to have a one-bag solution is to compromise on comfort at either end of the spectrum, being a bit too warm in summer (you’ll need to vent the bag, in fact, you’ll probably have to lie on top of it), and maybe a bit chilly in winter (you’ll need to done all your clothes and sleep with a hot water bottle). The classic 3 season bag fulfils this role pretty well, if you keep your activities to the UK, as here conditions are generally mild enough all year round these days (neither too hot nor too cold) that this type of bag is adequate 90% of the time. If this is what you want then there are tons of really great sleeping bags on the market that make ideal UK all-round bags, with stand out models including Mountain Equipments Frostline, Marmot Helium, PHD Diamir 500 and Rab Quantum 600, and many others.
The problem is that as climbers we are becoming increasingly more sophisticated in our gear choices, meaning that now we want a bag that will do far more than just keep us warm in the UK, using it also for slogging up Elbrus or ski touring in China, yet still be light enough for the KIMM, Polaris or a long alpine route with minimalist bivy gear. At the same time, as consumers, we just aren’t ready to compromise anymore, and like all other items of gear (rock boots, rucksacks, tents) climbers now want to buy specialist items of gear to fill each niche, whereas only 10 years ago you’d have had one piece of gear that did everything.
One way to achieve this is to view your sleeping bag as a system, just like your clothes, layering it to suit different conditions. This way you’re able to tailor your bag to its intended purpose more easily, and so build a true system that will work well for both 1 season use, right through to 4 season suffering.
For the last few years, I’ve been using various modular sleeping systems, both to give greater flexibility, and often to get the most out of the bags filling (matching down with synthetic for example). I started using this approach when climbing El Cap, as I would use a thinner bag low on the wall where it was hot, and then double it up with another light bag as I got higher, or if it got stormy. This approach worked really well and had the added bonus that you still had two bags if your partner dropped theirs off the portaledge (I’ve seen this happen twice). I soon started using the two-bag system in more hostile places, such as in the Alps, Patagonia and Alaska, finding it’s possible to build a lightweight and compact system that worked better than a one bag option. On the Lafiale route on the Dru in 2002, I used a 3 season Mountain Hardwear bag synthetic bag with a Western Mountaineering Highlite bag inside, which worked really well, even when the synthetic bag started going mouldy with damp. In the same year, I used the same concept in Patagonia…although with not such good results, as neither bag was quite up to open bivvys at -30oC (and the rest!), especially when the down bag got wet.
The basic idea is to use a very light and compact close fitting 1 or 2 seasons down bag, and match it with a 2 or sometimes 3 season outer bag (or 3 seasons down bag with a 1 season synthetic). The combined weight of both bags will be under 2 kg and will be around 10% heavier than a one-stop 4 season bag.
Generally, synthetic bags are larger than most small down bags, meaning they mate together well, and they give the added bonus of being cheaper (you may be able to just use your inner bag most of the time or buy the cheaper outer bag first or visa versa), and more able to cope with moisture (from without and within), making them an ideal shell. To further improve this shell effect I’ve often chosen synthetic bags with a water-resistant outer, which means I can often dispense with a bivvy bag, saving several hundred grams. The synthetic bag both increases the warmth of the overall system, and also protects the inner bag, as it’s much more resistant to the creep of dampness. The bags damp warmth also means it helps to keep the inner bag free of moisture, with the warm inner bag drying the outer bag in return. All in all this approach give you a system with better survivability in hostile conditions than a traditional one bag system.
Another bonus is that the bags can be split, meaning you have a superlight down option when needed, or a heavier weight synthetic option for mild damp conditions. The right combination should be able to cope with any conditions you may encounter, just like a traditional layering approach to clothing.
One thing I’ve often done is leave the down bag in its stuff sack when forced into my bag with damp or iced clothing, allowing it to melt or dry before getting into my own inner bag. Being splittable also gives the option to go lighter but wear more clothes, and a well-dressed climber will be fine for a night or two in a lightweight bag for a summer alpine route, or a single 2+ season synthetic bag for full-on gnarly climbing (where the bag may become full of snow and ice). Yet once back on the flat ground both bags can be joined for a good nights sleep. This system is great for base camps, as you leave your outer bag behind and take the inner on your climb (a trick often used by polar or Himalayan climbers), which in turn helps to dry the down bag on your return, as the synthetic bag will keep you warm, and allow the down bag to slowly dry inside it, something not easy to do with a single wet down bag.
The lightweight inner bag should be as simple but possible, lightweight and close-fitting. You should have minimal clothing on inside this bag, with duvets etc being placed between the inner and the outer. Standard 300-gram bags work best, but you may want a slightly warmer bag if you feel the cold, or want to get more use out of it as a stand-alone bag (going for a 400 to 500-gram fill weight). Luckily there and literally tons of great bags on the market these days. Material wise nearly all the super light bags have lightweight non-water-resistant outers, which are fine, but some more hardcore users may wish to get a bag with a more water-resistant outer. Getting such a bag increase weight a little, but with an increase in insulation longevity, and if you’re forced into the bag in poor weather (where your clothes may be snowy or damp), you have the option of using the bag inside out, with the water resistance on the inside.
Another option is to use a top bag, rather than a full bag, as you don’t really need bottom insulation (remember that heat rises, it doesn’t fall), and your sleeping mats insulate your bottom half, along with the bottom of the outer bag, when combined in cold conditions.
People always want to know if the top bag concept works? Well having used it, and knowing other climbers who’ve used it, the answer is yes, but it’s not as nice as a full bag, but it is considerably lighter. Paul Ramsden used one for the first time this summer in the Alps, climbing the Jorasses and he found the Rab Top bag both warm, comfortable and fantastically compact.
Other options include half bags, such as the OMM PA1 (360g/ £120), which only has down on the bottom half, meaning you’d need to wear your down or synthetic jacket on top (or place it over yourself). This is a good concept but if the bags for all-around use, not just extreme climbs, then a plain bag or a top bag works best, as it’s not nice having to sleep in your grubby belay jacket every night. Below is a list of bags worth considering, and is in no way complete.
Note: I’ve left out the temperature ratings as I personally feel they are misleading, and bare little relevance in the real world. Call me sceptical, but the ratings are also one of the main selling points for bag manufactures, meaning they often appear to have been massaged. As a rough scale of filling versus temperature: 200g/10 C, 300g/5 C, 400g/ 0 C, 500g/ -5 C. These temperatures will increase or decrease by 20% depending on down quality, bag features (baffle design, neck baffle), and metabolic rate.
Rab has several really good inner bags for this kind of system, with their Quantum range being ideal. Of these bags, the best three are the Quantum Top Bag (Fill weight: 200g, Weight: 430g, Price: £130), the Quantum 250 Endurance (Fill weight: 250g, Weight: 630g, Price: £200), and the RAB Quantum 400 (Fill weight: 400g, Weight: 900g, Price: £250). Of these the Top bag is ideal if you want out and outperformance and the 400 is a great 2+ season bag in its own right (a good alpine summer bag), plus there’s a woman’s model, and it’s also available with a Pertex Endurance outer. If you want something a little more hardcore Rab’s Summit 300 1/2 zip (Fill weight: 300 g, Weight: 820g, Price: £170) is ideal, featuring a water-resistant Endurance outer (and endurance lined hood), and several features that make it a great summer alpine bag, or part of a hardcore system.
ME have been producing great bags forever, and perhaps people forget how cutting edge they are because of that (a little like Marmot). Their ultra classic Dewline 300 (Fill weight: 300 grams, Weight: 700g, Price: £145 ) remains one of the best lightweight bags around, being full of great features, water-resistant and top quality. If you want a bit more warmth and a borderline stand-alone all-around bag, then their Lightline Ultra 450 (Fill weight: 450g, Weight: 1100g, Price: £180) is another classic, and you’d be surprised how cold both these bags will allow you to go if you’re a warm sleeper. ME’s answer to Rabs Quantum range are their Helium bags, with their Helium 250 (Fill Weight: 250g, Weight: 600g, Price: £144 ) and Helium 400 (Fill weight: 400g, Weight: 810g, Price: £162) being top-notch.
For quite a while now Pete Hutchinson Designs have been setting the pace in super light down bags, with their Minimus (Fill weight: 300g Weight:464g, Price: £154) and minim (Fill weight: 400g Weight: 670g, Price: £196) starting of the crazy search for beyond featherweight bags. Both make ideal inner bags, plus they can both be modified easily when purchasing (water-resistant out, neck baffles, zips etc).
Marmot has been producing amazing bags forever, but in the UK they are still primarily known for their clothing. Their entry-level bag is the Arete (Fill weight: 300g Weight: 679g, Price: £140) is nice and well priced, but I’d recommend going for their better 800+ range, with their Atom bag (Fill weight: 300g, Weight: 453g, Price: £180), and Hydrogen Reg (Fill weight: 595g, Weight: 595g, Price: £215) being about as good as it gets.
Macpac has two very interesting bags in the shape of their EPIC 300 (Fill weight: 300g, Weight: 700g, Price: £200) and EPIC 450 (Fill weight:450g, Weight: 850g, Price: £235), which feature a taped endurance outer, short zip, and designed for the hardcore user. One thing I’ve found with these bags is that they can be pretty restrictive, which may be a problem if you’re tall, or need to get into the bag fully clothed. As with all bags that you may bivy in sitting, make sure it’s possible to do so before embarking on a route, as often it’s not Most bags are too short when wearing a helmet).
OMM (the new name for KIMM) have two small bags designed for marathon runners that might be worth checking out, in the form of the Mummery 1 ( Fill weight: 200g, Weight: 460g, Price: £165) and Mummery .5 (Fill weight: 220, Weight: 490g, Price: £175), with the .5 being of the most interest as it features a central half zip.
Like the other manufactures, MH have a very lightweight range of bags in the form of the Phantom, with the Phantom 45 (Fill weight: 200g, Weight: 480g, Price: £160) and Phantom 32 (Fill weight: 300g, Weight: 650g, Price: £180) being in the same category as the Rab Quantum bags. MH also make the excellent taped SL series of bags, which really keep the moisture out, with their Spectre SL (Fill weight: 450g, Weight: 1250g, Price: £280) being one of the best hardcore bags on the market.
North face’s Sub Kilo bag ( Fill Weight: 388g, Weight: 993g, Price: £130), fits the bill and is a nice bag with some interesting features (such as synthetic pads on the bottom to increase underside insulation), plus it’s a nice price.
The main problem with the outer bag is that although we’re spoiled for choice with inner bags, there are almost no proper technical synthetic bags on the market. There are bags that come close, but non that jump out. When buying an outer bag, make sure the bag is a good shape and fits your inner well.
Note: As with down bags the temperature rating is pretty useless for real-world use (perhaps even more so than down). The main reason is that synthetic fills tend to degrade quickly at first, as the fibres pack down, perhaps losing 5-10% of their initial loft in the first year, wear as down will not. As a rough guide for Polargaurd bags (which are long-lasting but not as warm per gram) 1000g/5 C, 1500g/ 0 C, 2000g/ -5 C, with Primaloft being about 30% warmer initially but dropping off faster to an equal warmth perhaps. Again good or bad design will increase or degrees warmth by as much as 20%.
Marmot has been making high-end synthetic bags for a long time, and their bags are far from caravan camping models. Their new Wave range of bags stand out in having a good performance, but with a really great price, with the Wave II (Weight: 1380g, Price: £60), and warmer Wave III (Weight: 1750g, Price: £70), coming out well in many tests, using overlapping waves of SpiraFil insulation rather than the more traditional Polargaurd insulation. Weight wise the Pounder (Weight: 453g, 5 C, Price: £100) and Pounder Plus (Weight: 963g, Price: £120), offer a much higher degree of performance, being about as light as you’ll find in a synthetic bag. The only downside is the filling (Primaloft Sport) tends to need more care than the tougher (but heavier and less down like Polargaurd), as it’s not a continuous filament. This means it’s vital to store it loosely and look after it more like a down bag.
ME have a big range of synthetic bags, but unfortunately, the brilliant elasticised inner system on their 2 top bags probably reduces the effectiveness of a two-bag system (as used on their Stella Sleepwalker and Moonwalker bags). This leaves their entry-level Firewalker bags such as the Firewalker I (Weight: 1200g, Price: £60) and Firewalker II (Weight: 1420g, Price: £70), and their new Mithril I (Weight: 1340g, Price: £70 ) and Mithril II (Weight: 1340g, Price: £80) bags, which feature a reflective polar filling that improves thermal performance over a standard filling.
Ajungilak have been making top-level synthetic bags for a long time, with their Kompakt range probably being one of the most respected bags on the market. Their Kompakt summer (Weight: 890g, Price £80) and Kompakt Spring (1100g, Price: £90) are probably two of the best bags on the market, with their MTI filling providing the same performance as Primaloft, and are ideal out bags.
TNF make a large of synthetic bags, but of them perhaps the best for this kind of use is their Orion bag (Weight: 1070g, Price: £135), a well designed and trim Primaloft bag, that would work well on its own right, as well as paired with a down inner bag.
The twin bag system sounds like a great idea, the answer to your prayers, but of course, there’s a price to pay. There is a slight increase in combined weight, cost and perhaps bulk, and some people just can’t handle being trussed up in a close-fitting inner bag, but long term performance tends to make up for this, and the combined price is less than 4 season bag and less weighty than a 4 season synthetic bag.
The main problem is that there just aren’t any really great synthetic bags on the market, as manufactures’ just don’t see the point. Unfortunately, it’s a chicken and egg situation, where we need a company like Rab, Mountain Equipment or Moutainhardwear to bring out such a model so people can buy it. Ideally, someone would make a dedicated two-bag system…but maybe I’m just dreaming?