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Aaron Davis
(ardavis324) - F
Pack liner trash bag as feet VBL for sleeping? on 02/11/2014 13:12:12 MST Print View

Don't really have any other use for the plastic compactor bag pack liner, and somewhere I read it could be used as a vapor barrier liner. Wanted to explore that idea here.


I understand VBLs are most useful in multiple day cold weather conditions to keep insulation lofty... but would this make a difference or be worth it during average 3 season conditions?

Would it boost the effective warmth of my quilt on a cold night?

Edited by ardavis324 on 02/11/2014 13:15:04 MST.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Pack liner trash bag as feet VBL for sleeping? on 02/11/2014 13:28:04 MST Print View

If you are talking about 'average 3 season conditions', then you don't need a VBL. It might in fact do more harm than good, creating and trapping a lot of perspiration.

Cheers

Ian Van Halen
(IDBLOOM) - MLife

Locale: PNW
Re: Pack liner trash bag as feet VBL for sleeping? on 02/11/2014 14:45:41 MST Print View

Hi Aaron,

I learned that trick in the Army (for my feet) and it works well for me. I often recommend it for people who are having issues with cold feet at night as a potential lightweight solution. If you are using a garbage bag liner in your pack, then there's no weight penalty to use it as a dual-use item.

Only way to know if it works and for what temperature ranges it would be appropriate for you is to give it a try. Seems some people struggle with cold feet worse than others so kind of a YMMV thing IMO YOLO AWOL etc etc.

"Would it boost the effective warmth of my quilt on a cold night?"

Your thread title seems to be directed at the feet so if the only issue you are having is cold feet, then yes. Others have mentioned using garbage bags as a full VBL liner; I've never tried that so I can't answer that question.

Rafi Harzahav
(rhz10) - F

Locale: SF Bay Area
Using pack liner above or below sleeping pad? on 02/12/2014 10:16:32 MST Print View

Is there any insulating value at all in spreading a plastic pack liner on top of or below my sleeping pad?

Thanks.

Roger Dodger
(RogerDodger) - F

Locale: Wess Siide
Re: Pack liner trash bag as feet VBL for sleeping? on 02/12/2014 10:32:05 MST Print View

50/50
plus: traps warm air
minus: traps condensation too, greenhouse effect.
damp wet feet in warm humid air will get colder than
dry feet in cold air

as Les Stroud often says: you sweat, you die.
and the parody: you perspire, you expire.

presumably from hypothermia when all the environment conditions exist.

Ian Van Halen
(IDBLOOM) - MLife

Locale: PNW
Re: Using pack liner above or below sleeping pad? on 02/12/2014 11:49:44 MST Print View

For clarification, my suggestion is to put the bag/VBL inside the quilt/sleeping bag and not on the outside. I suspect using a non-breathable bag on the outside of the sleep system may temporarily add some warmth but at the cost of saturating the down and losing loft over time.

Matt Dirksen
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: Using pack liner above or below sleeping pad? on 02/14/2014 11:29:39 MST Print View

Hi Rafi,

Theoretically, yes. According to what I could find, a single layer of 3-6 mil polyethylene film has a measured R-valule of .87. Not much, but it could help a little (and slightly reduce the risk of puncturing your sleeping pad, if that might be a concern).

I suspect it is more useful as a make-shif vbl, even though I doubt the convective heat loss could ever be properly managed with a "trash bag" vbl setup.

best,

Matt

Hiking Malto
(gg-man) - F
VBL on 02/14/2014 11:39:16 MST Print View

If you are sweating, you are using too much insulation. VBL creates a high humidity environment not a high perspiration environment when used correctly.

The main concern I would have with using a bag would be not trapping the humidity in the VBL. The high humidity would be free to exit the trash bag into the rest of your sleep system. In this respect, bread bags or equivalent would be far better. And this can be used well above freezing to help keep feet warm. I have found this to be extremely effective.

Edited by gg-man on 02/14/2014 11:41:46 MST.

michael levi
(M.L) - F

Locale: W-Never Eat Soggy (W)affles
vbl on 02/19/2014 00:32:15 MST Print View

I think VBL is good on nights 30* and under.

Baselayer
+
plastic poncho/ cuben kilt/ garbage bag
+
lay poncho over body, stick feet in garbage bag.

Just draping a 2oz $1 poncho over my body under sleeping quilt added a huge boost of warmth. Its not going to be as warm compared to sealing plastic around you but you wont risk sweating.

I felt like all the precious heat that was escaping my body on a 10* night was captured in the plastic as it was rising up and out of my quilt. I didnt sleep well that night because I was still cold, but it was much better when I got the plastic out and did a VBL.

Glenn S
(Glenn64) - M

Locale: Snowhere, MN
Humidity on 02/19/2014 01:29:23 MST Print View

Kinda depends on the relative humidity I think. If it's a cold dry night, then your body moisture will be literally sucked through your bag like a wick. Losing heat both by convection and evaporation as latent energy. On a cold damp night however, I don't see a VBL being of much use, since it wouldn't really stop conductive loss at all anyway and if the air is already saturated, all you'll get is condensation.

I'm no scientist, just a wrench monkey, but it seems to me that's how it works. I do of course, reserve the right to be completely wrong.

Hiking Malto
(gg-man) - F
Re: Humidity on 02/19/2014 05:38:55 MST Print View

"Kinda depends on the relative humidity I think. If it's a cold dry night, then your body moisture will be literally sucked through your bag like a wick. Losing heat both by convection and evaporation as latent energy. On a cold damp night however, I don't see a VBL being of much use, since it wouldn't really stop conductive loss at all anyway and if the air is already saturated, all you'll get is condensation."

Where you are wrong is that there will be a micro environment created both inside your bag and also inside the VBL. Since a VBL reduces/eliminates moisture going through your bag there will be no condensation regardless of relative humidity. There have been extensive discussions on here regarding dew point and where condensation occurs. If condensation (dew point) occurs on the inside layer of your bag or VBL you have serious problems. (I can't even think of a scenario where that could happen short of ridiculousness such as using wind sheet material as a sleeping bag and sleeping in a very warm down jacket which basically then turns your jacket into a sleeping bag with arms.)

Clayton Black
(Jivaro) - MLife
Re: Pack liner trash bag as feet VBL for sleeping? on 02/19/2014 05:59:31 MST Print View

Off topic a bit but before I bought my Integral Designs Event Wedge Bivy for sleeping on mountains I had a catastrophic fail of a tent I shouldn't have been in at 14200 feet. I was able to cover my head but my feet were being blasted by rain and wind. Pulled out my compactor bag liner and slid it over my feet and slept cozy the rest of the night.

Luckily I was in a synthetic bag and not down or I would have wetted (is that a word?) out.

I've experimented lightly with VBL barriers in cold wet near freezing conditions in mountainous terrain but mostly ended up overheating. Plastic bags over my feet in unexpected snow does help though.

Edited to add: Thinking more about my past situation I did put on my rain jacket and pants so VBL played a bigger part in keeping me warm while sleeping than I remembered. I also remember being wet warm and toasty until I had to crawl out of my wet womb in the morning and then couldn't wait for 1) a coffee and 2) get my wet tail down the mountain.

Edited by Jivaro on 02/19/2014 06:10:01 MST.

Glenn S
(Glenn64) - M

Locale: Snowhere, MN
Re: Re: Humidity on 02/19/2014 06:36:55 MST Print View

"...there will be no condensation regardless of relative humidity." OK, I'm pretty sure they're closely connected.

"If condensation (dew point) occurs on the inside layer of your bag or VBL you have serious problems." I'd go along with that, maybe I didn't state it quite right, I didn't mean on the inside.

Hiking Malto
(gg-man) - F
Re: Re: Re: Humidity on 02/19/2014 08:45:14 MST Print View

Glenn,
Almost by definition you can't have condensation with VBL. If there is no moisture escaping from your body then there will be no condensation at least from moisture coming from your body. So if there is no moisture then outside humidity becomes irrelevant.

Alex Herron
(AlexHerron) - F

Locale: Front Range
Oh trash bags on 02/19/2014 21:28:35 MST Print View

I love using trash bags. I guess I am a trashy kind of person, but I always bring two still attached to each other from the roll. 1.1oz They form a larger 26 inch wide 7 feet long ground sheet typically. This is with two layers of complete waterproofness. None of that soaking you get with silnylon. Anyway you could also use it as a liner if it floats you boat, but you could also use it as a vapor barrier and I will at this point in the thread only give outrageous support for doing this. For me with two I can make a pseudo poncho for my top half and encase my lower have as described above. BUT also you can use the trashbage as emergency bag cover for your feet of the bag if the rain is coming in a little and you didnt pitch your tiny tarp very well... that never happens right? ahem. All I am trying to say... there are a few things on my gear list where I am just amazed with all the things I can do with them. Cheap plastic trash bags are up there... with poncho tarps... handkerchiefs/buffs... good stuff. Makes you feel all mcgyvery and stuff.

Jerry Smith
(crossfox21) - F

Locale: East Oregon
How about your rain/wind shell? on 05/01/2014 22:59:41 MDT Print View

I have heard good results with this