Vapor Barrier Liners and Waterproof Materials

If you need a mild boost in warmth I find that something as simple as a plastic poncho draped over your body works wonders. This is used over your baselayer, and under the sleeping bag.

Personally I used a cuben cloud kilt last trip when I was pushing the limit of my 30 deg quilt. I think if you were to wear a rain jacket/ something form fitting to bed you would get perspiration/ wetness. A full VBL is what it is though, its just NOT (imo) comfortable unless you really need the heat.

Thanks Michael. The main objective would be to keep my perspiration from getting into my down sleeping bag, which I understand in cold conditions gets trapped inside the baffles deteriorating it's insulating capabilities. In my mind, I was hoping if I use a thin rain jacket/pants inside out wearing the waterproof side against my skin (actually against a baselayer), it would prevent my perspiration from reaching the sleeping bag's down fibers.

Furthermore, since some of these breathable waterproof fabrics, in my basic understanding, allow air to flow in one direction by using them backwards the airflow would be reversed from the sleeping bag into my body which would help with the "clammines" normally associated with VBL.

Again, I'm not expert on these matters and that is why I'm reaching to the knowledge on this forums which I have in high regard.

I think vapor barrier is good for very low temperatures (like below 20 F?) for many days

I've tried it a little for a few days above 20 F and it did something but non vapor barrier worked just as good

you want the vapor barrier near your skin – everything between vapor barrier and your skin will get damp

Mario,

On my last winter trip I was worried about the same thing, here's what I did.

Let me set the seen, it was in Yosimite Park the temps at night got down into the low single digits, me and my son were in a 2 man tent with the vestibules just laying on the tent, not staked out, I wanted to keep as much heat in as possible, but I also new this was going to create a lot of condensation inside the tent.

My solution, I made a syn. quilt the week before to take with me on this trip.

Inside the tent I was in my bivy I needed all the extra warmth I could get,
since I only had a 20* down quilt.

I put my down quilt over me first, then I put my syn. quilt over the down quilt and between the bivy, in the morning the syn. quilt was soaked, almost to the point that you could ring it out, but me and my down quilt were dry and toasty warm all night.

In the morning I just hung the syn. quilt out in the sun for about 30 minutes and it was dry and ready to pack away, I made the syn. quilt with black material for this reason, so the sun would help it dry faster.

Hope this helps.

Jack

Well the intended purpose is correct, anyway.

"Furthermore, since some of these breathable waterproof fabrics, in my basic understanding, allow air to flow in one direction by using them backwards the airflow would be reversed from the sleeping bag into my body which would help with the "clammines" normally associated with VBL."
This is basically incorrect. A WPB fabric makes a poor VBL. The WPB works with temperature/vapor pressure to move water vapor (perspiration) away from your body. It pretty much doesn't matter which way you wear it.
A good series of articles here:
http://www.backpackinglight.com/cgi-bin/backpackinglight/orwm_2011_wrapup_waterproof-breathable_technologies.html
This is NOT what you want from a vapor barrier. There is a pretty good atricle outlining when and where to use them here:
http://www.backpackinglight.com/cgi-bin/backpackinglight/vapor_barrier_liners.html

You will see that the difference is very fundamental.

Thank you guys. I do appreciate your feedback.

Jerry, yes I need a system for multiday outings where temperature it will be below 20 degrees. If I use a VBL I will make sure is close to my skin (BTW, thank you for all those MYOG tutorials).

Jack, I really like your approach. I may modify it a little though…. I do normally carry on this kind of outings a Patagonia DAS parka which is fairly light and has synthetic insulation. Sometimes when it gets really cold, I wear it inside my sleeping bag, but based in your advice, I guess it would make more sense to drape it over my sleeping bag. This would achieve three things 1) boost the warm of my system; 2) move the dew point outside of my down sleeping bag into a quick drying/synthetic insulating layer (i.e My DAS Parka or your Synthetic over quilt) 3) Minimize weight / bulk by making use of gear I already carry. I may create a small synthetic quilt for my legs, but this may not be needed since my lower body perspires at a much lower rate than my upper body.

James, thanks for the links. I was familiar with Andrew Skurka’s article but obviously incorrect about how breathable waterproof membranes work. I knew there was a flaw on my logic when after several searches on these forums I never saw my proposed approach as an alternative.

I can’t wait for the mountains to start to dress in white.

Cheers

Mario

Mario,

The object behind the syn. quilt was,
1. Perspiration or condensation will pass through the down bag.
2. Condesation passes through the breathable fabric of the syn. quilt.
3. Condensation gets trapped in the syn. insulation and does not return to your down quilt or your body

The only penalty I paid was the extra weight of the syn. quilt which was minimal, my syn. quilt was made with Apex 2.5 and the whole thing weighed about 14 oz and was only good for 45* temp. on its own, so with the 20* down quilt and my syn. 45* quilt I was very warm, I think inside the tent it only got down into the high teens, low twenty's even though the temp outside was 5* or lower.

Jack