Bushwalk Australia

Hi all, Vapour barriers are an effective way of increasing the warmth of a sleep system, however they don't seem to have a very broad adoption, at least in Australia. I was thinking recently that it would be possible to make some rather nice vapour barrier sleeping bag liners using the latest lightweight waterproof fabrics, both for use along with my quilts but also with any other sleeping bag/quilt system. So I'm interested to gauge interest and hear people's thought about this idea.

I'm thinking of a design that's similar to a mummy bag in shape but with no hood with the intention that the user would cinch the liner around the neck as needed. I'd also include a short side zip for easier entry/exit and a venting option. With a fabric like the 0.93 oz/sq.yd. Membrane silpoly from Ripstop by the Roll I think the weight of a standard size liner would be in the range of 110g - 120g.

If there's some interest I could get ahold of some fabric and give them a go.

How does what you propose compare with the SOL Escape Bivy:

http://www.amazon.com/SOL-Escape-Breath ... B00GT5FL4A

...that's the Lite one, weighs 156 grams. I have the normal version, with hood. It's big enough to put a sleeping bag inside.

The SOL is going to be a partial VB and if my experiences using the Tyvek are any indication they work rather well.
The total VB would also have to be reflective with a long life to compete with the WM version

I might be mistaken but doesn't the Sol cover the sleeping bag. VB goes inside the bag between the bag and you!


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Giddy_up wrote:I might be mistaken but doesn't the Sol cover the sleeping bag. VB goes inside the bag between the bag and you!

Actually it doesn't seem to matter how big a VB is cut, you save a few grams if it's cut smaller but then it isn't able to be used as an emergency SB cover

Good point MD.


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Moondog55 wrote:

Giddy_up wrote:I might be mistaken but doesn't the Sol cover the sleeping bag. VB goes inside the bag between the bag and you!

Actually it doesn't seem to matter how big a VB is cut, you save a few grams if it's cut smaller but then it isn't able to be used as an emergency SB cover

A VB is designed to go under an insulating layer, surely, as ( the name suggests) it prevents convective heat loss via moisture and air transmission.
Sticking one over the sleeping bag would render the insulation less useful as it would become damp, increasing conductive heat loss and making the insulation much less useful over subsequent days - unless it can be dried out.

A sleeping cover, ie bivvy bag is usually vapour permeable for that reason.

Interesting idea undercling-mike.

I am one of the few people that swears by vapour barriers to sleep in - even in Australian conditions (certainly below freezing but even a bit above). They add a lot of warmth, they do an amazing job of keeping the down dry over multiple nights (so your sleeping bag or quilt doesn't collapse by the end of the trip and loose some of its insulating power) and they are also a great emergency item. Use one and I am confident you can get away with a lighter sleeping bag (or be warmer / have more error margin for your weight carried - whichever way round you prefer). Far lighter, more effective and more useful for other situations that one of those warmth booster liners (e.g. S2S) that some use.

I have used the SOL emergency bivy - the non-breathable one (http://www.adventuremedicalkits.com/survival/shelter/survive-outdoors-longer-emergency-bivvy.html). Cheap, light and works fine over a number of nights (not too delicate) though you need to be a bit careful. I would recommend to anyone going to a colder climate walk (e.g. nights to zero or below) to take one for insurance against colder than expected weather, as your emergency space blanket and also as an emergency bivy (better than nothing for a night). Cheap enough (in the vicinity of $25 delivered to your door) and light enough (110g) to be a 'why not?' argument.

I now have the Western Mountaineering Hotsac. Nicer to live in (not so plasticy) and much more durable but heavier (130g) and much more expensive (would do well to buy one and have it delivered for Au$150).

So if you would like to make one - they are your two benchmark competitors in terms of price, durability and weight. I have thought before it would be interesting to see if a light cuben fibre VPL could be made (all taped). However cost would be astronomical and probably only save a few 10s of grams against the benchmarks above. But you are right that any waterproof (not breathable) fabric could work - but balanced against weight, price and comfort.

Personally if you pursue this project features I would consider:

- No zipper (it is unnecessary weight, cost, complication and I can see myself snagging it on the fabric of my sleeping bag doing it up), just make the cut plenty roomy so it is easy to crawl into (and you want room around the feet too for your shoes / boots etc. to go inside the bag so they don't freeze up). I don't see much advantage of a tight fit for warmth here (unlike a sleeping bag itself) - with no air exchange inside the VPL bag you heat up and fully humidify the air very quickly. No hood but including a cinch cord around the neck is spot-on.
- The perfect material would be very light and completely waterproof/non-breathable, but ideally have a soft inside feel. Plastic works but is not so pleasant against the skin. The WM material doesn't feel plasticy, but isn't fully soft/absorbative like either. The WM has the extra bonus/gimmick? of the reflective treatment on the inside. Something like the liner material on many waterproof breathable rainjackets would be the nicest to sleep in - but most likely something like this would add too much cost and weight.
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Somehow, if you are going to have a market, you are going to have to better WM for price, with similar or better weight, comfort and durability. If you come up with something better in features, weight etc than WM at a higher price, you will appeal to such a small fragment of an already small market (small in the USA, tiny in Australia) that you will do well to sell 3 of the things in your lifetime!

The other option is to try and educate the market to how useful these things are and how to manage them to be comfortable. It seems to me that a steady stream of very good outdoors people (the latest probably being Andrew Skurka) have been trying to do this since at least the 70s, but with minimal success. Maybe one day there will be a big enlightenment in the market, but I wouldn't bet my mortgage on it.

That's true, but the size of the VB was what was asked about
As the fabric used to make a VB is so light what size it is cut has very little bearing on the finished weight
If you are stuck out on the hill with no tent, windy and lots of wet snow the optimum choice in those circumstances is to use the VB as a bivvy cover.
WM cut their VB larger to allow for that possibility
In Antarctica and the Far North it isn't unusual for the sleeping bag to be used with a totally waterproof cover in conjunction with the VB. Silnylon being usually much lighter than a WPB
In the same way my Tyvek SB cover is cut quite large but no quite big enough to fit over my expedition cut bag but I have used it as a liner and even tho it is breathable it has lower breathability than the SB itself; therefore it acts as a partial VB and is warmer than for example a silk liner
Interestingly it is also lighter than my silk liner
Many of the original bivvy bags were waterproof, it better to be warm and damp than cold and wet and you wore your waterproofs inside your sleeping bag as the VB part of the system [ this is assuming you had a sleeping bag with you] the essential thing being to keep the wet and rain off you.
I think you missed the word "Emergency" in my post
In my experience there is a world of difference between a bivvy bag and a sleeping bag cover although the distinction has become blurred in the last decade or so

Got to agree with you Moondog55 - having a bit of extra size makes it a better (multiuse) item for little penalty in practice.

nq111, I am also a big advocate of VB in Australian conditions, even warmer ones.

On more than one occasion I have woken up in my quilt from being to warm. Because I use a VB the inside is wet and on a couple of occasions dripping. All this moisture would have made its way into my quilt.

Mike I think it's one of those things that you may need to get a few out there so to speak and get people providing feedback on their experiences using a VB. Once people see and understand just how wet their own body is making their bags you may see an emerging market. As you know I use Cuben and swear by it, the caveat being that I did all my shopping when the AUD was $1.10


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Yep, a VB should go inside your insulating layer. The general recommendation for a VB sleeping bag liner is to wear just a light base layer inside it (for comfort I believe).

Vapour barriers work largely by creating a humid microclimate around your body. Your body regulates the humidity around the skin by releasing water vapour, this can be up to 1L over the course of a night and this water vapour carries a lot of heat away with it (think evaporative cooling). In a humid environment your body will release much less vapour than in a dry environment, greatly reducing this mode of heat loss. Another important benefit of a vapour barrier is that it prevents this moisture from your body from getting into your insulation and reducing its effectiveness.

If you use a somewhat permeable or breathable material such as the SOL bivy or Tyvek as a partial VB it will still reduce the rate of vapour transfer and maintain a humid microclimate, the effect will just be stronger with a fully impermeable material.

For use as a VB sleeping bag liner a reflective coating will not be of any benefit because the VB is inside of your insulation and the temperature difference between the VB material and your skin/base layer will be small, meaning radiative heat transfer between the two is small and in any case the sleeping bag insulation, either down or synthetic, is actually very good at preventing radiative heat loss. For a space blanket or emergency bivy that might be used on its own the situation is obviously different.

The Western Mountaineering hotsac vapour barrier liner looks pretty nice but they're quite expensive at just a few dollars less than US$100 before you consider shipping, and the reflective coating isn't of any benefit for use as a liner. I'd think it'd be possible to produce something quite a bit cheaper and made out of a coated woven material so also more durable than something like the SOL escape lite, which apparently is quite delicate.

I've never been in conditions that warranted using a VBL but the idea is fascinating. Having never tried it I've wondered about answering a call of nature in the middle of the night -- you'd be dressed in wet base layers, not the ideal starting point for a trip outside in the cold. And in the morning you'd start out the day wet. Or maybe you don't get as wet as I imagine.

Andrew Skurka has a pretty good write up about it. He prefers VBL clothing which I think resolves my concern above, although it leaves me wondering how much effort one has to expend during the day adjusting clothing. Here's a snippet from his blog:

An effective VBL system needs to consist of either a sleeping bag liner or a full multi-piece VBL clothing suit. It is redundant and unnecessary to use both a VBL liner and a VBL suit. Personally, I prefer to wear VBL clothing, which has a few advantages. First, I can use a lighter sleeping bag because I can sleep with all of my clothes on—a base layer between my skin and VBL, then all of my other layers outside the VBL. With a VBL liner I can only sleep in my base layer garments; otherwise all of my layers would get wet. Second, I already have all of my clothes on in the morning when I wake up, which saves time and body warmth. Even if I brought all of my non-base layer clothes into my sleeping bag but outside of a VBL liner, I will lose a lot of heat when I try to change into them. And third, I keep all of my clothing dry at night and during the day, except for my base layers, which may become slightly moist with perspiration. If I were to rely exclusively on a VBL bag liner, perspiration would enter and become trapped in my insulated jacket and pants while I wear them during rest stops or in camp. The one downfall with VBL clothing is that I need to have a complete VBL suit, which is heavier and more complex than a bag liner. In the long term, my sleeping bag could be compromised if I am not completely covered with VBL’s. A complete suit would include socks, pants, jacket, gloves, and a hat or balaclava.

Been a lot of discussion since I started writing my last post! At least it's a topic which is of some interest here. I wouldn't expect to sell loads of these things but I was just thinking it would be worth seeing if a compelling product could be developed, and if so make them to order at whatever rate of demand there might be.

I think the lightweight coated fabric would feel somewhat like the hotsac material (which is a coated woven material) rather than the more plastic material of the emergency products and it should be plenty durable since the base fabric is similar to a lightweight sleeping bag/quilt fabric. So it'd be an item made for long term use and hopefully with a good 'feel' in the product category. Probably at about half the cost to get hold of a hotsac. Zipper would be optional.

One limitation is that for efficient fabric use the fabric width would limit the size you could make it. I was thinking of something with similar dimensions to the FF Vireo bag.

Vapour barrier clothing would be a good option but much more complicated to produce and it probably comes down to personal preference as to what system people will prefer.

Heya Mike,

I actually think there would be a greater demand for VB clothing rather than VB sleeping bag liners. A VB sleeping bag liner can already be easily improvised cheaply with a large rubbish bag (what I have done up until now), but it is hard to find a quick substitute for VB clothing without buying something from the US or making something yourself. In addition, VB clothing has a number of advantages over a VB sleeping bag liner in terms of practicality and versatility. You can't wear extra layers of clothing at night at risk of them getting wet with a VB sleeping bag liner, and you also can't protect any insulation layers from perspiration during the day with a bag liner like you can with VB clothes. I'm not sure if you've read this article before by Andrew Skurka, but there are a number of relevant points he raises within (http://andrewskurka.com/2011/vapor-barr ... plication/). There also seems to be a very small market making functionally apt VB clothing which could be potentially capitalised on (both here and internationally). I'm currently part way through making some VB clothing for this season...I'll post the finished result in the MYOG section once I'm done if you're interested

I'll be keen to see what you come up with FootTrack, what material are you using?

I don't think it'd be practical for me to produce vapour barrier clothing at this stage, it's a niche market and everyone's a different size/shape. There would have to be a big enough market to warrant mass production to get the price down, maybe it could be done with a huge marketing/education campaign by a bigger company.

There are plenty of ways to improvise a vapour barrier, obviously a rubbish bag or emergency bivvy for a liner or cheap non-breathable rainwear or a tyvek suit for clothing, nothing wrong with any of these options but I'm thinking someone who's decided on a vapour barrier as part of their system would be willing to look at a more durable product that offers a better 'feel' and optimised design.

If looking to promote vapour barriers towards any particular user group then maybe very cold sleepers would be a good starting place, it'd give them an alternative to going with ever warmer sleeping bags and constantly battling to avoid being cold could be a good motivator to experiment. Cold sleepers are probably less likely to overheat and sweat in the liner as well. Of course a VB will increase warmth for all users and allow them to potentially bring less insulation.

I also think that when ever this topic comes about there is the inevitable "use a garbage bag" scenario. Sure you can but for me, walking is as much about comfort and good rest as it is about the actual walk. Sleeping in a garbage bag puts most off, myself included but I have a VB system that works, comfortable and is light.

The other thing with a VB is the simple fact that it does make a difference and actually adds a level of safety to any sleeping system.

The discussion has been interesting and very informative and I am keen to see what might materialize from it.


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Orion wrote:I've never been in conditions that warranted using a VBL but the idea is fascinating. Having never tried it I've wondered about answering a call of nature in the middle of the night -- you'd be dressed in wet base layers, not the ideal starting point for a trip outside in the cold. And in the morning you'd start out the day wet. Or maybe you don't get as wet as I imagine.

What conditions 'warrant' a VPL is a matter of individual opinion and experience. I think VPL for sleeping is perfect for the almost freezing, constantly damp conditions of Tassie (helps heaps keeping the sleeping bag dry and puffy) but others may disagree. I read plenty say they would only consider it in conditions well below freezing - but not sure if any of these people have played around with it in warmer conditions. However to be fair I am pretty sure I am more tolerant than others being using to sleeping in warm, humid conditions here in North QLD (have used VPL to sleep in conditions down to + 8 degrees once just to see - was ok for me but probably didn't achieve much either!).

Yeah, you don't get as wet as you imagine (or to be exact, I don't ). I find a get a quick chill from some minor dampness in my baselayers as soon as I get out of my bag, but it is gone by the time I put an extra layer of light fleece or whatever over the top (which then enables me to dry out whilst I have breakfast / get ready for the day). Probably similar to the dampness you have in your baselayers after gentle walking (not noticeably sweating) in steadu rain for a hour under a breathable rainshell. If you read the experts on the matter they write that if you are getting really wet the problem is too much insulation (not inherently the VPL). Exactly as Giddy_up said - you probably don't realise overheating and the amount of moisture being put into your down without a VPL. But also, you will be warmer with a VPL so will need to learn to use less insulation (all else being constant) anyway. E.g. I don't zip up my sleeping bag anywhere as much as I would without the VPL.

I believe that VPL clothes would be heavier, more expensive and complicated as well as not having the same multifunctional benefits as a simple liner. For those doing really cold and technical stuff (e.g. Arctic / Antarctic) - absolutely - but otherwise not. Though I do love my VPL socks in the snow

nq111 hit the money with his answer
Sales will be minimal and would depend mainly on being price competitive.
For some reason or other even if the physics says NOT I find that a reflective inner face feels warmer
There are other makers of VB liners and compared to PHD the WM Hotsac looks cheap.
The downside to using a VB is that you can't take a systems approach to the sleeping insulation unless you also wear a full VB suit against your skin
If you decide to use a VB you would need to wear the lightest weight synthetic underwear you can find against your ski. Wool doesn't work with a VB system
Getting out of bed in the AM isn't all that painful even at -25C, there is very little actual water in the underwear, after all the VB stops insensible perspiration and what there is there flashes off very very quickly
I can tell you that a VB shirt over polypro underwear works very well with a light fleece and a waterproof parka; not a goretex but a real waterproof works well down around -12C just sitting around not doing much when warm from just having stopped walking

I sleep in a wool base layer MD with no detrimental effects.

Can you enlighten me on the synthetic use reason?


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Giddy_up wrote:I sleep in a wool base layer MD with no detrimental effects.

Can you enlighten me on the synthetic use reason?

Simply because it dries so much faster; you use the lightest weight wool?
It doesn't work for me using woollen underwear is all I can say and that was the advice I received 30 years ago when I first starting to use a VB shirt

Yes I do sleep in the very lightest fabric, can't tell you the weight but "icebreaker"

The synthetic is interesting and I shall do a little digging.


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Well, undercling-mike, it at least looks like you may have a few beta testers available if you do try making some of these things

Hi Mike,

Great to see discussion and interest in VBL. I personally have not tried any although I have experienced friends who swear by them for extreme winter and arctic trips. I am though genuinely interested in experimenting with them for future winter trips and am keen to hear how you go with producing them.

By the way I absolutely love my new -8 quilt that you made. From my perspective I wouldn't change anything. Despite the warm Tassie summer I have recently taken it to Mt Anne, Mt Field and down the Collingwood River and will take it on the South Coast Track in another week or so.

Cheers

nq111 wrote:

Orion wrote:I've never been in conditions that warranted using a VBL...

What conditions 'warrant' a VPL is a matter of individual opinion and experience. I think VPL for sleeping is perfect for the almost freezing, constantly damp conditions of Tassie (helps heaps keeping the sleeping bag dry and puffy) but others may disagree.

Point taken. What I meant was that there was never a time where I wished for the advantage of a VBL. I've never had the pleasure of doing a longer trip in Tasmania in the winter. The vast majority of my experiences have been in a relatively dry climate (California Sierra) where dampness in my sleeping bag has been predominantly due to external moisture sources. But admittedly there have been times where the opposite was true; it's just never been a big enough problem to require my attention. If using a VBL came without any downsides we'd all be using them.

I actually have used VBL liners in my boots a few times in -15 to -20°C conditions, although that was mainly because I had lousy plastic boots back then. As I recall my feet really stank on those trips.

I find the discussion on VB clothes for active use somewhat curious. This is only used for extremely cold conditions, from what I have read - and even then Andrew Skurka, for example, emphasises hte need to tailor exertion so as to not sweat too much. Can you imagine what it would be like wearing a VB suit in Australia whilst walking/skiing in anything but a blizzard? I would be comatose with dehydration within the hour. makes perfect sense for static activities, however.

The idea of a VB quilt or bag seems to make perfect sense though. rather than have a VB 'suit' to sleep in, or a VB bag and VB bag cover, what about a sleeping bag/quilt with silnylon instead of standard nylon as the outer?

Have to admit, being a cold sleeper and wanting to protect my sleeping bag, and doing all my walking in Tassie these days, this is something I've been thinking about recently. Not sure if it would work for me as I hate waking up damp, but I want to at least try it out.
No zip, just a shaped bag. The sort of material Mike's talking about would be pretty light.

I am interested in VB liner but I am not sure I would want a mummy shape. A part of the reason I use a quilt is because I cant sleep while if I am restricted.

I made a silnylon bivy and even at this size it is too restrictive for me to sleep in. (the width of the material was a limiting factor) I never did bother carrying it as an emergency bivy so I cut it up and used the material for other things.

slparker wrote:I find the discussion on VB clothes for active use somewhat curious. This is only used for extremely cold conditions, from what I have read - and even then Andrew Skurka, for example, emphasises hte need to tailor exertion so as to not sweat too much. Can you imagine what it would be like wearing a VB suit in Australia whilst walking/skiing in anything but a blizzard? I would be comatose with dehydration within the hour. makes perfect sense for static activities, however.

The idea of a VB quilt or bag seems to make perfect sense though. rather than have a VB 'suit' to sleep in, or a VB bag and VB bag cover, what about a sleeping bag/quilt with silnylon instead of standard nylon as the outer?

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You don't sweat any more than normal tho and as such dehydration isn't an issue, if you have pit-zips on your parka it may help if all of your layers have matching pit zips for ventilation but my own VB shirts didn't have them and I never found the lack thereof a problem

You can get a dew point app for most devices. It's interesting to play with and you get some surprising results. 5 degrees C with 85-90% humidity will see a dew point of 4 degrees C

So the drop required is very small for the dew point to be reached and start to be trapped in your bag.

I would imagine that the above scenario can be reached in Tassie and the Alps regularly. Even in QLD those sorts of figures can be found in the cooler months at 2-3-400 meters of elevation.


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