Vapor Barrier question

>I find eVent more breathable than Epic in all conditions and truly waterproof, which Epic isn't.

Maybe, I haven't used an eVent bivy. I know that Epic is not 100% waterproof, but since I only use the bivy in a tent, I'm not too concerned. I really don't think tha fabric is the issue though. For whatever reason, when it gets cold enough that you body moisture hits dew point before it leaves your bag, you've got problems. I've had this problem even without a bivy, but not as bad.

Midwinter Yellowstone: Maybe 8 hours of daylight, not counting time packing up and setting up camp, highs between -10 and -20…the wine never thawed, and chocolate was like eating concrete. We had to heat the wine in a pot to make it drinkable (and drink it really fast oh dear). Not much chance to dry a bag while trying to fit in 5-6 hours skiing.

I was also using the Inuit trick of rolling your bag up the instant you get up to push as much of the warm, moist air out of it. It could have been much worse if I hadn't done this!

It was after that trip that I fell in love with VBL clothing…I think a VBL might work OK with a WPB shelled bag, as long as the outside of the bag didn't get too wet to pack with your down. On that trip (and many others), I've often had lots of 'snow' on the bag due to respiration.

The reason why I brought up eVent and mentioned all conditions is that there is some commentary by Ryan Jordan (several places in this forum as well) in the state of the market on bivy sacks that discusses the shortfall of Epic in cold conditions where the pores ultimately freeze and plug.

I have had a lot of success with eVent but granted, not at -40.

Another item for consideration: this article at BPL…

http://www.backpackinglight.com/cgi-bin/backpackinglight/wet_weather_performance_down_vs_synth_vests.html

argues that "higher volumes of down and a less breathable shell will reduce the wet weather performance of a down garment. The Down Inner jacket has a higher volume of down than the Flash and lofts to 2.8 inches of double layer loft. Its shell material is MontBell's Ballistic nylon. Ballistic nylon threads are calendared. They are heated, then flattened and widened. This improves abrasion resistance and reduces down leakage, but also reduces breathability and slows the drying rate of the Down Inner jacket."

Though there are of course many variables to consider, and we are transitioning from jackets to bags, this article argues there is a link between water resistance of outer material and drying rate of insulation. Admittedly, this is probably leading to another thread- when using a vb liner or clothing, the hope is never to have to deal with significant moisture in down in the first place! With an effective vb in place, outer material type should make little difference, at least in regards to the issue of body-generated moisture. Thus, with a vb in place, the discussion of SB shell material or bivy selection IN THEORY can focus solely on the function of dealing with any exterior moisture. In practice, and particularly with vb clothing, I like a system that can deal with some degree of internal moisture. Andrew Skurka's article about his amazing winter trips is great reading on these ideas.

Yes, in THEORY, if using a VBL, you don't need your SB outer material to breathe at all. It could be made out of cuben and still do the job. No need to use heavier eVent.

Yes – no need to use eVent unless you want durability and a higher hydrostatic head, which is irrelevant in a tent.

Except that a non-breathable WP shell would limit the use of the bag to winter. It's no fun sleeping in a VBL in summer just to keep your bag from getting soaked from the inside.

>unless you want durability and a higher hydrostatic head

You mean using your sleeping bag outside without cover?? I can't imagine wanting to do this, but it's a choice you're free to make. I would consider it in an eVent bivy bag, but not a standalone eVent shelled bag.

Yes, in theory, in harsh cold, with a perfect vb system, the sleeping bag fabric could be almost anything. As you say, in practical application, theory meets practice- the vb isn't perfect for any number of reasons, moisture finds its way into the SB insulation somehow, and in any event an SB with waterproof fabric would be very limited in its applications.

I have found it useful to ask my SB only to be an SB- to provide necessary insulation while sleeping in a form that is as lightweight as possible and able to be maintained, and especially kept dry, while backpacking- highly breathable material, perhaps with a DWR. The vb answers the question of moisture from the inside when this becomes relevant in cold temperatures, while the question of exterior moisture can be answered in any number of ways: various bivy designs (momentum, eVent, goretex…), tarps, single or double wall tents, and on down the line. Thus, I have not yet encountered conditions where I would want the shell of my SB to be anything other than lightweight and very breathable. Asking an SB to do more than this seems to always come with a sacrifice of flexibility IMHO- though in some conditions, this sacrifice may be worthwhile.

"You mean using your sleeping bag outside without cover?? I can't imagine wanting to do this, but it's a choice you're free to make. I would consider it in an eVent bivy bag, but not a standalone eVent shelled bag."

Sorry – thought you meant a cuben bivy.

>Sorry – thought you meant a cuben bivy.

Even so, the lightest eVent is 2oz/yd. If you used an equivalent weight cuben (the heaviest cuben I've seen is 1.5oz/yd, but they prolly make heavier), I'll bet it would be pretty darned tough AND very waterproof. But no, I meant a cuben shelled bag. I'm actually thinking about making a quilt out of it, but that would be cuben lined as well, so kinda a built in VBL, but I'm still not 100% committed…

Yes but Cuben is not at all breathable. Doesn't this bring us full circle to the condensation problem?

Patagonia chose not to use eVent due to durability issues.

I don't see how it would be MORE durable than cubenfiber, even
in a lighter weight. The lightest eVent I know of is still
over 2 ounces per square yard.

I used a Goretex shelled Northface bag for 5 years of full
time guiding and never had a problem with condensation.
It did eventually de-laminate, but Northface replaced it.

It was called the Gold Kazoo.

In very cold conditions, (-10 F) when out for 4 weeks at a
time, I used a polarguard overbag, which worked very well.

I don't know how the Goretex shell would have worked at
-40 as the outer layer but-

I have used Goretex bivys as stand alone shelter on long trips
to -5. At times I used a VBL, which did help a lot in increasing warmth for the
long haul, but I can think of only 2 times I noticed
serious condensation issues with the Goretex bivy, while
under the stars and no VBL. Both times I was sleeping
within a few feet of water and the humidity was
very high.

>Yes but Cuben is not at all breathable. Doesn't this bring us full circle to the condensation problem?

The cuben comment was in reference to the *theory* that in a perfect VBL system you wouldn't need a breathable fabric at all, but also to point out that not all cuben is fragile and leaky as you implied:

>no need to use eVent unless you want durability and a higher hydrostatic head, which is irrelevant in a tent.

Maybe the 0.36oz per yard stuff is, but it is unfair to compare a 2oz per yard fabric to a 0.36oz per yard fabric when it comes to durability and waterproofness.

As mentioned before David, you were lucky, or living the ideal conditions, if you never had condensation problems with a GoreTex covered bag. Neither Roger or myself have a vested interest in making up condensation issues with this system. His wife and I both noticed problems, and in different conditions. At minus 40, my situation could have been deadly if habitation wasn't close by. Then again, I've also had condensation in a momentum covered bivy when the conditions are right (as you experienced, high humidity etc…), so sometimes it's inevitable without a VBL. The trick is to know when you are going to experience those conditions and be prepared. If you've only seen it once in a long life in the hills, then you must live in a very dry but not too cold environment.

The more I think on this topic, the more motivated I am to make that cuben quilt!

Hi –

New member here. As a personal note, I don't like VBL clothing. Other than sleeping, I find them as a single use item. Don't work as a windshell, because they don't breath.

I use a Integral Designs Sleeping Bag VB Liner in sub-freezing weather along with my WM UltraLite Sleeping Bag (20F) and a water proof bivy. As a single use item, it weighs 6.1 oz, and is lighter than most VBL clothing set-ups I have found. I also sleep better with the liner, rather than VBL clothes. The only purpose of the VBL is to control condensation on my bag. In warmer weather, when I need a bivy and condensation is not an issue, I use a MLD Soul Bivy Zip under a poncho. This set-up really works well for me.

– Nick

"Maybe the 0.36oz per yard stuff is, but it is unfair to compare a 2oz per yard fabric to a 0.36oz per yard fabric when it comes to durability and waterproofness."

No it isn't. If I want something with more durability and waterproofness then I will go for 2 oz eVent.

@David Olsen – please provide the tear strength and hydrostatic head for the cuben you are referring to. Thanks,

>No it isn't. If I want something with more durability and waterproofness then I will go for 2 oz eVent.

You're assuming the eVent is more durable and waterprrof than 2oz per yard cuben? I seriously doubt it…anyone have the stats on 2oz cuben???

I don't think lucky. During the 5 or so years I had the Gold
Kazoo, I slept in it the whole time, even when I wasn't
working. I was in the Winds, the Sierra Nevada, the North
and Central Cascades, Eastern Oregon in Winter, Joshua Tree
in Winter, Arkansa, Colorado, and the Olympics of Washington.
While much of it was dryer places, not all and most of my
time was during shoulder or winter trips. The Gore product
may have been their first generation version without the
plastic protective film. I bought the bag in 1981.

The bivysacks I have used tho, were more recent Goretex2.
I have used bivys of Bion2, which was less breathable
and had little problems with that too.

Maybe I don't sweat like some.

I don't have a hydrostatic head for Cuben fiber.
Maybe I will play with some of the scraps of eVent and
Cuben I have.

>Maybe I don't sweat like some.

Maybe. Or maybe you run on the hot side, so your perspiration never reaches the dew point before it hits the outer layer. Certainly, for me to have significant condensation inside a Momentum bivy indicates that I am not generating enough heat to push the vapour through. Maybe it's a female thing…we DO have lower metabolic rates than the guys (on average), but also tend to sweat less (especially on cold nights). It's not like I'm going "Oh my gosh, it's minus 20 and Im roasting in here"! Maybe my bags had too much loft for me to heat completely??? Doesn't matter-bivy or not, I go for a VBL when temps get substantially sub-freezing.

David O, do you have a variety of cuben fabric weights to play with?

I have experience with Gore Dryloft vs Gore-tex covered sleeping bags over 11 nights where the temps were -20 to -10 C.

We didn't have VBL's with us. I had the dryloft bag, and I would simply leave it zipped up in the double wall tent for 15-30 minutes before stuffing it. The loss of loft over the trip was not noticeable (we dried out in a hut on the 5th night).

My two tentmates had Gore-tex covered bags – they wetted out by the end of the first and sixth nights, and they slept cold the rest of the trip, other than at the hut.

Reading what Mike Clelland writes here at BPL (and Jo Anne Creore in her book), I think I could get my Dryloft bag to work at -30C for an extended period, without VBL. -40C? Probably not. Not with my current skill set.

But for the last 10 years I've used a VBL bag. I was using an FF VBL (sylnylon with a half zip) with polypro and it worked very well for me. This winter I tried a Hot Sac with thin merino wool, and I started to get wet. I don't know if it's the Hot Sac or the wool, so I will have to try the different combos. Sure would like to keep the wool.

I tried the Dancing Light raingear as VBL clothing, but it didn't work for me. I'm small, and I lose heat too quickly through my extremities. Like wearing gloves when you need a mitt.

Some friends suggested that I make a non-breathable shelled bag, since I use the VBL bag – but that doesn't work. When I get to a hut, I can't use the VBL without getting soaked.

If anyone using VBL found they got more wet when using wool rather than synthetic underwear, please let me know.

I just got back from a day of ski touring in sustained -25C weather (sometimes a little warmer, sometimes a little colder)over the weekend and had mixed reviews on a Golite Vapor Vest that I was wearing (silnylon on the back, thin breathable nylon on the frount).
Wearing that vest overtop a Cap 2 t-shirt and under a Cap 4 and R1 pullover and a EPIC hoody, I REALLY liked the vest for stoping the wind and for keeping my back insulation dryish.
Still I found that the moistere trapped at my back stayed there and eventually became clammy, a little chilling and very uncomfortable. I was wearing a pack most of the time and would like to try again w/o the vest.
Still, not sure what to think of the whole exparmint.
The clothing was apropreat to the temprature/effort involved

edit: Just a thought:

Wear your WPB jacket/pants under your VBL.

This will add warmth, while at the same time keep you dry under your VBL.

Does anyone have tips with integrating insulating clothing into a sleep system while using a vapor barrier liner (not clothes)?

..

What Huzefa posts about wearing WPB clothing inside a VB liner is interesting but I think misguided. WPB clothing only transports moisture from high humidity to low. As soon as you have a very high humidity inside the VB liner then the WPB clothing will cease transporting moisture and the moisture will back up into your insulating clothing.

I think a better option if you are using a VB liner is to simply drape your insulating clothing on top of the liner, or even on top of your SB.