Vapor barrier in sleeping bag Pro's & con's?

[kgd]

Skammer raised a good point about vapor barriers used with sleeping bags in Fonly's thread about survival shelters. I haven't used these, but have known about them for some time and it makes sense. However, whenever somebody mentions Vapor Barrier, someone else pipes up about the risk.

Frankly, I don't know what those risks really are. I recognize that you can heat up in them and get sweaty. My recollection is that it is recommended you sleep in them in the nude so that your clothing doesn't get sweaty too. However, if your insulation is maintained and you stay warm then this shouldn't be the problem. The main claim to them amounts to the North Pole treckers, whose bags, without a liner build up enough ice in them to weight as much as the man itself. Of course nobody likes to wake up sweaty, unless that is you are with a female companion

Perhaps this thread can explore the merits and problems with using a vapor barrier with your sleeping bag. What are the brands out there? What are the set up issues with them? After a week of camping do you have reservations crawling into the "armpit" for another night?

 

[borrowed time]

from an article in the now defunct Survival Journal, i bought a US, GI body bag as a sort-of bivy. as they are sealed very well you can sweat in them, bad at times' if the temp goes up.

they do lock in the heat and lock out the rain fairly well and they are relitively cheap and light to carry. i only use it in the summer as a shelter when i go on minimalist camping trips in the mountains.

------ ERic

 

[mdauben]

I haven't used these, but have known about them for some time and it makes sense.

I have used vapor barriers a few times in winter camping and I think they provide a definite advantage if you know how to use them properly.

Frankly, I don't know what those risks really are. I recognize that you can heat up in them and get sweaty.

Its true that you can overheat if your gear to too warm for the temps, but if kept in check its not a huge problem. Even under ideal temperature conditions, you will sweat in one, and you will get at least damp. This is referred to as "insenitable"(?) sweat, and occurs even when you do not requre sweat for cooling. The advantage of the vapor barrier is that if this moisture collects inside the vapor barrier, it does not have much impact on your warmth. If it condenses or even freezed within the insulation of your sleeping bag, it will significantly reduce the insulating quality of the bag and can lead to problems staying warm.

In my experience, my sleeping bag always ended up damp after a couple days of cold weather camping w/o a vapor barrier. With the vapor barrier my bag stayed dry, warmer and much more comfortable despite the minor issue of the dampness inside the VB.

The main claim to them amounts to the North Pole treckers, whose bags, without a liner build up enough ice in them to weight as much as the man itself.

Now, IMHO its true this is really only an issue in fairly extreme cold weather camping (well below freezing). It does not however require true "arctic" conditons, as you can find below zero weather in many areas of the continental US during winter. I've done some winter camping in WI, MI and MN, not to mention some early "Fall" camping in AK where nightime temps dropped into the teens or less. In just "cool" winter weather the vapor barrier does not really offer much advantage.

 

[skammer]

Where I find the advantage of vapor barriers is you can reduce your weight and bulk of gear and still get some warmth out of the bag.

The -10 bag I use with a VB on outside and inside of the bag brings it down to -25-30. This is a big advantage in weight and bulk savings.

This is how I work my system. I wear silk weight wicking underwear head to toe then I put a thin layer of cotton over this. This serves 2 purposes, when the wicking underwear wicks the cotton allows the moisture somewhere to go and absorb instead of rolling around the VB inside. 2/ it keeps the underware amazingly dry thus keeping you comfortable. As was mentioned it also keeps your bag insulation dry so it can do what its supposed to do.

I carry 1 set of silk weight underware and wear one. The cotton does freeze during the day and the moisture can be knocked off it in very cold conditions (freeze drying kind of).

FYI, In very cold conditions I also employ the same deal in my boots for the feet, works great and your liners dont get wet .

All this will dehydrate you faster so plan for this.

Skam

 

[cuphead]

Hrm this is a good thread, for instance 3 weeks ago I went winter camping with a -20 Hybrid MEC bag and a bivy.
There's a lot of talk about how it condensates and you get soaked... but thats only if you don't think it through. for instance, I stripped down to my thermal layer and I dont cover my face with the bag/bivy.. simply to avoid the moisture on my breath to soak me from within.. If you respect that... I think you'll be find.

I was in temps close to -15 deg celcius and never slept any better in my life on a camping trip
Also want to mention I had no shelter setup through that week-end except for that bag/bivy setup. Nothing like sleeping in a snow bank

 

[valcas1]

Skammer,

What are you using for your vapor barrier on the inside and outside your bag? I am very interested in this info.

Thanks

Paul

 

[Ravaillac]

Pro:
Completly remove the moisture management prob

Con:
You'll be backing in your own sweat and body odours.

Honestly, probably worth considering.

Edit:
Btw, also remind me of an inuit techniques read about in some book.
They used a double sided fur blanket. The thing collected ice during the night. When it was saturated with ice, they just flipped it over. In the morning, all they add to do was hang it outside, wait sometim and then shake the ice away which is possible since fur relies on hairs rather then enclosed insulation like most modern sleeping systems. Does seem pretty versatile to me. Should work with any insulation.
Wonder if it wasn't Buffalo from UK that had that sort of gear.

 

[skammer]

Skammer,

What are you using for your vapor barrier on the inside and outside your bag? I am very interested in this info.

Thanks

Paul

I use the AMK heatsheet emergency bivi for both inside and outside. They are lightweight, reflective which captures radiant heat and they are pretty durable, they are also reparable unlike mylar .


Skam

 

[kage]

I have a sil-nylon vapor barrier from Feathered Friends that I use during winter climbs.
I have only used vapor barrier bags successfully in temps well below freezing, otherwise I get soaking wet in condensation and sweat. During the winter I find them to be ideal. My winter bag is rated at -18 F and with a vapor barrier liner and a hot water bottle I have slept in -40 degree temps (in a tent or bivy sack) without any problems.

 

[mdauben]

What are you using for your vapor barrier on the inside and outside your bag?

There are companies that make coated nylon bag liners for use as vapor barriers that you can get from most comprehensive outdoor outfitters. On the outside a bivy sack or bag cover is my ususal (the VB liner also allows you to use a less expensive waterproof cover, instead of a gortex one, or a breatable one with a tarp).

If you are really cheap, my first experiment with using a VB liner was using a 55gal drum liner (large industrial strenght garbage bag) that I got for free from work.

 

[Ravaillac]

My winter bag is rated at -18 F and with a vapor barrier liner and a hot water bottle I have slept in -40 degree temps (in a tent or bivy sack) without any problems.

I'm not tempted for regular use, but with some trash bag, as emergency tool, it does get very interesting.

 

[kgd]

Great information guys. Sorry for the post and run thread. I got really busy at work, had one of my grad. students write a kick ass little paper. Totally unexpected as it was her first crack at a writeup. I wasn't expected much, but when I read her stuff my little publication bell went a ringing....

Anyhow, Skammer - really great information. Basically, a low weight solution to cold weather camping. You make the choice of weather to use the vapor liner or not before going to bed. If its cold, then you do and at worst you get a bit clammy at night. If you decide not to, well it was a better weight alternative to packing in a more insulated stand alone bag.

Skammer - sorry dude - I pictured you in the nude in this thing and not in silky underwear. I'm not sure which vision presents a worse mental image! Please don't tell me those jammies are bright red So, my understanding is that the wicking silk helps distribute that sweat around your body rather than concentrating in a dripping mess at whereever your lowest point of the sleeping bag is right?

Thanks for everybodies considered answers!

 

[1Tracker]

MDauben, you did a pretty thorough job with your info on this. Skammer added to it.

The reason I mention the caveat is there are 15 yr olds reading this stuff all day and night. We don't need them going off with a trash bag without the knowledge to self rescue if need be. that was my reason in Skammers shelter thread fro mentioning the dangers.

I've used commercially sold VB gear for almost 25 years, and some improvised bags over the years too. If you know how to modulate them you can work them to your advantage, they are not for everyone as some will find out.

 

[skammer]

Skammer - sorry dude - I pictured you in the nude in this thing and not in silky underwear. I'm not sure which vision presents a worse mental image! Please don't tell me those jammies are bright red So, my understanding is that the wicking silk helps distribute that sweat around your body rather than concentrating in a dripping mess at whereever your lowest point of the sleeping bag is right?

HaHa, When I say silk its not a robe with a cigar a la Hef .

I mean silk "weight" underwear, as in a wicking layer the same thickness as silk. If you go to MEC and say silkweight they will know exactly what you mean.
By wicking the moisture from the skin to the cotton layer over it where it is absorbed it is much more comfortable and your skin stays much drier.

I can just picture me with silk PJ's on and a hot totty in the nalgene.

Skam