Winter sleeping systems, trying weird new shit like VBLs

We’re having a warm spell of weather in Stockholm right now. This could be a timely reminder that everything comes to an end, and soon we will have to pack way our skates and skis and igloos, and get ready for the Swedish Summer, coming in the form of clouds of pollen, clouds of mosquitos and clouds. It’s also a timely reminder that we should get our priorities straight and leave jobs, partners and families to one side, don our wooly hats and get out into the snow as much as possible before it’s all gone.

Back-country skiing through the burnt landscape of Tyresta national park.

The good times I’ve had so far this season owe a lot to the gear that made harsh conditions comfortable, none more so than the sleep system. No matter how good gear you have in terms of rucksacks, skis, gloves, tents and all that shit, if you’re not getting a solid nights sleep at the end of the day, you will have a shitty trip. A bad sleeping bag means a rough night, and I am sure everyone who has tried Winter camping has had one of those nights. Those nights when the weatherman was on crack and forecasted warm temperatures, instead it drops below -30 C° and you end up trying to sleep through the night with insufficiently warm gear. Shivering, chilled to the bone, twisting and turning to try and find some warmer position. Waiting hour after interminable hour until the cold grey fingers of dawn start to reach into your tent. Fucking. Horrible. To really enjoy Winter camping the quality of your sleeping-gear has to be excellent.

Unfortunately Winter sleeping systems can be a pain in the neck. Synthetic bags are reliable, they can be literally soaking wet and yet still functionally retain heat. However they are also heavy, heavy enough that if you want to be out below -10 °C, you’ll need around 2 kgs of sleeping bag. And they compress like shit, even a warm-weather synthetic bag takes up a lot of space. Down bags are half the weight and compress much better but they turn from thick fluffy marshmallows of warmth into thin dribbling rags if they get too wet.

The terrifying wet surface of a down-quilt in the morning.

If the temperatures are well below 0 °C, and if you happen to be the kind of person that is largely made up of water, then you can count on waking up in a bag a few dozen grammes heavier with condensation from the sweat and breath of your nocturnal slumber. I occasionally do submission wrestling competitions, and when cutting weight it was always the morning weighting that was most rewarding, it’s not unusual to drop a kilo during the night. My girlfriend hasn’t complained about me shitting the bed in years, so the weight loss must be due to water vapour. That’s a litre of water a night, some of it ending up in your down bag.

A few millilitres of water in your down reduces loft a little, but is not a problem for an overnight trip. On longer trips you can try drying your bag out in the mornings, but in Winter it’s not effective and sometimes the weather can be an uncooperative asshole. You can also buy bags with heavier waterproof fabrics, but this negates the nice weight savings from down, and reduces loft. You can also have a down under-quilt, and throw a synthetic over-quilt on top of that. The theory is that the moisture from your body passes through the down quilt without condensing due to the insulation of the synthetic quilt. And then when it hits the synthetic quilt it condenses there, but that doesn’t matter because it’s synthetic. I don’t fully get the logic, down is not a good insulator by itself, it functions by lofting up and trapping air. The amount it lofts up is proportional to how effective it is, and sticking a heavy synthetic quilt on top of a down quilt just squishes some of that air layer and reduces its efficiency.

At a certain point of wetness, down bags just give up and collapse, and you wake freezing and shivering and in danger of hypothermia. There are plenty of reports in various hiking blogs about rough nights encountered after the collapse of a down bag. For example Maz goes through it here and Henrik has a go here, neither of them liked it much.

What I ended up doing (after a lot of playing around) was to use an extra layer, called a vapour-barrier layer (VBL). The idea is simple, you stick a waterproof layer between your repulsive clammy moist body and your delicate down quilt. The moisture can’t get to the quilt so it can’t collapse it. “Wait a moment!” you might well say, “surely that’s just like wearing a black plastic bag or something, won’t you get all disgusting and sweaty inside it?”. Bingo, that’s exactly what it’s like and exactly what happens. You get in your VBL and after an hour it’s like lying in a pool of your own stinking, goopy sweat. In fact it is lying in a pool of your own stinking, goopy sweat. Sexy!

That’s the idea at its most basic, some people advocate the idea that your skin also stops sweating after a while in a VBL, that after a certain saturation point your skin realises that sweating more is not a good idea and just gives up. This is bollocks as far as I can tell (I’m a terrible cynic, if it’s not on pubmed I consider it folklore). There’s no need to dress up the idea, it works even if I do continue to sweat all night and that’s OK with me, it’s OK with me because it works. I decided to use the Adventure Medical S.O.L. Thermal Bivvy Sack as a VBL. It’s a light, non-woven nylon space blanket, totally wind and waterproof. It has some velcro around the edges to stick it together, and comes in a tiny shitty stuff-sack. It weights around 220 grammes and costs around 300 SEK.

The Winter sleeping system

The ground layer is the ever reliable Exped downmat 7, big fat valves that don’t freeze up like the smaller twist-caps on thermarests, built in pump so you don’t get breath-vapour condensing inside the mat and screwing up the down. I’ve had a slow leak with my downmat during Summer, but a dunk in the bath revealed the hole, and a dot of rubber cement from the repair kit sealed it up. There’s a great set of instructions to read on repairing a hole here, courtesy of Exped. I think my girlfriend put the hole there to stop me from going camping. Or to trick me into having a bath.

It’s hard to hype the Exped downmats, they deservedly have a hell of a reputation. Super-insulating, incredibly comfortable, reliable, resilient and full of clever design details. They’re overkill for warmer weather, but I hate to buy things that I already own and have no intention of buying smaller lighter mats for Summer. As I use it all year round I designed my MYOG bivy-bag to fit the exped 7 exactly. The bivy-bag has been in use for months, but I still haven’t finished working on it.

The end of the footbox (and half the top) of the bivy-bag are made of a breathable 240 g/sqm material. Apparently it’s a bionic material, that opens its pores at warm temperatures and closes them at lower temperatures. Not totally sure how effective it is but will keep an eye on it. The rest of the top, sides and bottom are made of thinner, lighter non-breathable 90 g/sqm PU-coated nylon. All from


All the seams are tape-sealed on the inside, with extremtextil’s seam sealing tape.

When sewing the materials together, I placed one material over the other, folded them over and sewed that fold, so the seam holds the folded material in a sandwich, hopefully making it more waterproof than just flat sewing them together (demonstrated below). This seam probably has a name but I don’t know it.


The bathtub corners are also designed to be waterproof, instead of cutting the material and sewing it, I folded the edges together and sewed and seam-sealed them together at the top.

The zip is for entry-exit if the head of the bag ever gets finished, it’s a YKK waterproof zip from extremtextil. The material above the zip folds down over the zip partially, then the inside fold is sewn and taped, so water running down from above will not get near the seam, it will drip onto the zip. Then below the zip it’s the opposite, the material folds on the inside of the zip, which is taped on the outside so that water can’t get near that seam either. Looks a little uglier with the tape outside but looks aren’t important, as my mom used to tell me, what’s important is that as long as the water is mostly coming from above, it won’t even get near the sealed seams.

The seam between breathable and non-breathable material on the top is sealed inside only, although I might run across the seam with seam sealer solution if it leaks.

The hood of the bivy-bag is the last part to finish, it’s completely open at the moment. I’m just not sure what to do with it yet! It actually works pretty well as it is, but I will try and finish it up in a better way over Summer when bugs become a problem. Currently I just pull it over my head, it’s long enough that no weather gets in.

The hood, draped over the shovel.

All the layers visible in the photo below. Outer layer is the blue breathable bivy-bag top, then the Warhammer black mamba down quilt, then the VBL, and finally a green silk liner.

In the mornings the VBL and the silk inner are wet, so I turn the VBL inside out and hang them over ski poles. They are both thin and non-absorbent and so dry in minutes if the weather is OK.

Below is a look at all the components wrapped up. I have no stuff-sack for the bivy-bag as it’s not completed yet. The down quilt packs away easily. The VBL is impossible to get back in the miniscule stuff sack with icey fingers. The Exped downmat is a goddamn miracle of design for packing away. No matter how shitty the conditions have been, no matter how frozen and unresponsive my fingers have been, I have always been able to get it rolled up and in the bag in one go. I love the way it packs away.

Theoretically before hitting the sack I can eat all the extra strong lamb vindaloo I want, sweat like a priest in a kindergarten, and yet the down will be safe from all my nocturnal emissions. In the morning I splash my way out of the VBL, twirl the silk liner around to dry, invert the VBL and mop away the sweat-soup with an old sock. And in practice that’s exactly what happens. The interior of the VBL is soaked, but it absorbs nothing and dries in minutes if left to drip. The silk liner absorbs very little and also dries relatively quickly, while the sensitive down bag remains bone dry. On top of all that I wear the cold-avenger to bed as well. The cold avenger is a nice fleece lined balaclava and detachable mask for very cold weather. The mask part has this plastic cup and a little ventilation gizmo that mixes your warm exhaled air with incoming cold air so you don’t get cold in your lungs.

The best thing about the cold avenger is how it makes you look like some kind of ski-ninja.

I got it for skiing and robbing banks but tried sleeping in it once to see if it would help controlling exhaled moisture. This made a clear difference. Without it I wake to a halo of frozen condensation around my head, stalactites hanging from my nostril hair (especially when sleeping without a shelter). With it there is no sign of condensation around my head, inside the mask though it’s pretty drippy. I started wearing the ‘hat’ part of the cold-avenger to keep my head warm (down quilts only come up to the neck, forcing you to rely on your day-time head warming gear to keep your head warm at night), and then tried the mask on when I saw the only damp parts of my quilt were at the head end, so then i started wearing the rubber mask part too. If you want to adopt the mask idea then I hope you have as much S&M experience as Tomás ‘The spankinator’ has, because some prudes do find it a little hard to sleep in a rubber mask.

Inside the mouthpiece, wetter than a nun in a candle shop.

Is a VBL worth the hassle?

Yeah, totally worth it. Downsides do exist, you might find it uncomfortable to sleep in a moist environment. Whatever is with you inside the VBL will get wet. If you are the hardcore ultralighter who wears all of his clothes to bed as part of the sleeping system, then you’re going to wake up with a lot of wet clothes. On the other hand, there is no need to wear clothes in the VBL. The Adventure Medical bag retains an insane amount of heat, so it does more for warming you up than a jacket will do. A base-layer is all you need, and if you’re using synthetic or wool for base-layer, then it getting clammy isn’t such a big deal. I’ve found so far that the silk-liner prevents my base-layer from getting very wet, it usually dries during breakfast.

You also have the problem of dealing with a wet VBL and liner. This is not a real disadvantage, it’s a far simpler problem to solve than drying out a quilt. You can wipe them down and hang them outside in good weather and they are dry in minutes, literally. Your down bag remains bone-dry, totally pristine. Wake up in the morning, stuff it in the stuff-sack and rest easy that it will allow you to rest easy in another 12 hours.

With a down quilt the VBL is capable of dealing with proper cold, and maybe with just the VBL and a liner you could have a hell of a light Summer sleeping system. I’ve only tried the VBL in Winter, and some people say in Summer a VBL is too clammy and wet, but I will try it out anyway and see how it goes in a few months.

The Adventure Medical S.O.L. Thermal Bivvy Sack.

I don’t think you need to buy this thing to have a VBL, you could easily make one from recycled plastic shopping bags, you can buy a roll of extra-large black plastic bags and use them, you could use a diving suit, or a gimp suit, or you could be all fancy and make a MYOG VBL from siliconised nylon or something. It’s a stupidly simple thing to make, easily DIYable. The Adventure Medical bag is pretty good though, if you don’t mind the cash. First off, it’s silent. No plastic sounds as you roll around in it. Secondly it has a soft, textile feel to it, so it’s a lot less disgusting when wet than a plastic bag would be. Thirdly, it has the claim that it reflects 80% of radiant heat (a typical adult gives off around 100 watts in radiant energy).

The bag lends itself to modification, it’s massive, so there is a lot of leeway to cut weight by cutting the bag to fit your size and sewing it up a bit. And I promise you won’t feel bad taking a knife to it, there is no fit or finish to this thing. The sewing is laughable and the velcro around the edges is just ridiculous. It would be hard to do a worse job.

The picture below shows the shoddy sewing, a tear already on the right side, and also shows how the hook velcro patches tend to grip onto the inner fabric.

Downsides apart from the dodgy sewing are the insanely shitty stuff-sack, it has to be the worst stuff-sack ever. You need masterful origami skills to repack the bag into the stuff-sack, it takes ages to do, and that’s when you’re at home, indoors, warm and dry. Doing it in the snow is just impossible. I plan to cut it to fit me better and then perhaps it will fit a little easier into the sack. We’ll see. I would reiterate the fact that this fabric is damn nice for a waterproof material, so all of these downsides are irrelevant to me, it’s premium VBL material and plenty of it, so well worth the small price.

Anyway, that’s enough nerdy shit about VBLs. Trying VBLs was a bit like having an enema, at first it felt really wrong and a little disgusting but then it felt really great and I want everyone else to try it too. Go and try it!

8 thoughts on “Winter sleeping systems, trying weird new shit like VBLs

  • February 19, 2011 at 4:05 am

    I've tried VBL on a recent winter skiing trip and found it very comfortable. Wearing a thin wool top + long johns felt only slightly clammy, and it kept me warm enough that I could occasionally vent out warm, moist air.

    Using silnylon with an aluminized layer, I made both a VBL bag and a VBL top quilt. The bag worked better, and it will be my choice, even though my down layer is a top quilt.

  • February 19, 2011 at 8:30 pm

    Genius post, I love your use of language! If the temperature returns below freezing in the next month this is my next experiment.

  • February 20, 2011 at 6:48 am

    Great post. Some top notch MYOGergy going on there! Never fancied VBL's myself. What was that Adrian Kronaur line? "Hot and wet. Mighty fine when you're with a lady but not so fine if you're in the jungle" Don't like the idea of sleeping wet and short of making a full suit from my kids pampers that's going to happen right. See how I get on in two weeks. I'm sure if my down collapses after four nights out I'll suddenly have a different perspective on VBL's.

    BTW I think your seam are felled seams.

  • February 21, 2011 at 5:13 am

    "my girlfriend hasn't complained about me shitting in the bed for years" – classic!

    great, fun post about VBLs. Your experience of geting soaked in them is not persuading me to try them at all, though! The idea of waking up wet in -30 scares the shit out of me!

  • February 21, 2011 at 1:43 pm

    Very entertaining post but I disagree on few parts.

    First, the down bag with a synthetic overbag works like a charm. In a very long run in extreme (I mean towards North Pole from Canadian high Artic in early March or so) the synthetic bag will end up being a big chunk of ice but the down bag will stay warm and comfortable. And the insulating value of the combination is not as simple as looking for the loft of the down bag.

    Some guys I know tested moisture accumulation by sleeping in a extreme cold laboratory in -60C. They managed to get around one kilo of moisture in the bag during one night! But I haven't got that much ice in my bags…

    A serious winter down bag seems to work adequately in serious winter conditions for a week or so. I slept five nights in a bag with 1420g of +680fp (European) down in it, in temps between -11C and -28C. As it was during the polar night there was no sun (and no wind) to dry it, so I didn't. That bag gathered a bit over 500g of frost during the five nights but it was only on the last night that it started to be a bit uncomfortable. I think one could do a week with only a down bag before having to dry it. And during late March and April the weather is usually good enough to grand one or two days when you can dry the bag in the sun so during a week with a down bag only I didn't notice any moisture problems as I dried the bag in the sun.

    And I also have mixed feelings toward Exped down mats. Nice and warm but having seem then malfunctioning in -30C, I can't trust them. Instead I take two or three CCF pads. Foolproof and warm enough. And snow is soft enough for a good sleep with that combination.

    I also tested a facemask but found it unnecessary at least down to -33C. Haven't slept in colder weather yet. It was nice to breath in warm air but the clammy feeling on my face wasn't worth it.

    I am interested to test VBL as it would be lighter than the synthetic overbag but during the dead of winter when it is necessary there is no chance to dry it, sun doesn't shine and if it's windy it's usually a blizzard. So, does the ice accumulate in the VBL or can you just shake if of after it's frozen?

  • February 21, 2011 at 3:17 pm

    Good and valid points, Jaako.

    It's interesting that you only use CCF pads, and that you had trouble with down mats. I've read a lot recently about down mats developing leaks.

    The synthetic overbag seems a sound solution to extend the amount of time one can use down.

    In the dead of winter though, if a synthetic bag becomes a block of ice, and a VBL might also freeze, is there any other solution? I would imagine that the water in the VBL would remain water and you could just pour it out. Still, a patina of moisture would remain, which would make it very unpleasant to crawl into late at night, especially without a baselayer.

    One thing is for certain thoug: different people have different needs for winter gear. Some swear by VBL. Some manage with down. Some get too hot, some too cold, using the same equipment in the same conditions. What works for one fails miserably for another. We can make generalisations, but until you try it in the field you can never know for sure.

    I suspect the guys you know in the lab got that much moisture in the bag because of a lack of air movement to aid moisture transportation. An interesting experiment, but somewhat unrealistic, I suspect.

    I wonder what Shackleton did!

  • February 21, 2011 at 8:53 pm

    Doug: Aluminium coated silnylon sounds great, where do you get it from? I wouldn’t mind trying to MYOG a VBL with something like that.

    Phil: I can highly recommend trying it out, I don’t know where the lower limit (temperature-wise) for a VBL is, I guess the advantage of having a dry quilt is only apparent below zero, but it’s a very effective insulating layer no matter the temperature.

    Dave: Thanks for the tip on the seams, it’s interesting at the moment with all the new terminology to learn in sewing/knitting. But it’s also occasionally frustrating to muddle my way through the sewing and then afterwards find out that my hours of experimentation could have been saved with a ten minute google search.

    Mark Roberts: I might have over-emphasised how wet it gets in the VBL, but yeah, even the tiniest bit of sweat at minus 30 is horribly chilling. Although when it gets that cold I am usually too cold to sweat and also am wearing everything I brought with me. As to your second question, if I remember correctly Shackleton had 5 kilo reindeer sleeping bags, but they went up to around 20 kilos with accumulated moisture, so I guess he might have given his right arm for a vapour barrier.

    Korpijaakko : Thanks for a really detailed reply. I appreciate that the synthetic over-quilt and down bag is a very dependable combination, it seems to be a good way to deal with moisture in very cold temperatures. I just play it down because I prefer the idea of a VBL. A synthetic over-quilt prevents condensation in the down, but you still get moisture freezing in the synthetic quilt, and you still get a build-up of weight because of that. You also do get some moisture building up in the down anyway, just not as much. The VBL idea is so attractive because attacks the root of the problem, preventing any moisture building up in any absorbent part of the sleeping system. You save weight by not carrying a moisture laden quilt, and the insulation provided by a VBL will really surprise you. Let’s not forget that the VBL I use is not sold as a VBL but as an emergency bivvy bag, it has a very high insulation with respect to its weight.

    Interesting to hear about the Exped mats failing, what part failed with them? I have had one bad night because of a slow leak (luckily in Spring), but normally even below 30 degrees I don't get problems. Although I guess there is nothing as reliable as a CCF mat 🙂 Hard to puncture one of those.

    It’s phrased as a joke in the article, but I am almost serious about S&M being a prerequisite for sleeping in a mask. I am lucky enough to fall asleep seconds after I get into my sleeping bag, no matter what. So occasionally sleeping in googles and a mask, with my head on some ski boots doesn’t cause me any restless nights, but I can appreciate that it is not for everyone.

    I am not sure about the answer to your question (If the VBL can be allowed to cool and then the frozen water inside it just shaken off), I have so far been quick in getting it dry as soon as I get out of the bag. However I am now seriously curious about this, it would be a way nicer solution, to leave the bag for a few minutes, turn it inside out and shake it. I am going on a trip up north this weekend and will give it a try.

  • February 22, 2011 at 1:00 pm

    Mark: "different people have different needs for winter gear" Very true!

    Tomas: "The VBL idea is so attractive because attacks the root of the problem" Most definitely so! I should give the VBL systems a try (as a sleeping bag liner and as socks) but haven't found time for it this winter because of preparations for a big trip…

    I haven't used Exped Down mats but couple of friends have had problems with the valves. Likely it is because some down gets stuck in the valve, causing a slow leak so that you wake up every two hours shivering and having to re-pump the mat. CCF requires a lot of space but is otherwise foolproof, so it suits also for me. 😉

    If you can shake the ice off the VBL then it would work well. I recon that if you sleep in your base layer only (as we bot seem to do), it dries out quickly when you throw a fleece and a down jacket on top of it.


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