I don't have this problem when I use one of my double wall (with inner mesh) tents.

Help me understand the ways a double wall tent makes a difference here. Some possibilities:

1. Avoiding moisture transfer from brushing against condensation on the underside of the fly and (up to a point) condensation dripping from the underside of the fly.


2. The tent's inner walls being a barrier to wind blown fog.


3. An enclosed tent holds heat better than a tarp (the old rule of thumb that the inside of the tent will be 10*F warmer than the outside on cold nights) thereby keeping the inside temperature above the dew point. Wouldn't that help be limited to only when the each night's conditions (temp and dew point) happen to be in "just the right combination"? Or are they typically in that range whenever it's cool/cold and near 100% humidity?

I would say you nailed it Jim, but i would rank your reasons in the opposite order. Pushing the dew point out to the inner tent wall most important. The other 2 can be simply dealt with by a decent water resistant shell on the bag.

Ventillating a shelter with 100% relative humidity cold air...wont do much for you, except cut down on internal surface condensation while making you colder, and potentially having a dewpoint inside your insulation.

Would seem that minimal ventillation in a single wall shelter might work to keep temp up , but the walls/roof will have severe condensation. But that might be preferable in calm conditions if it keeps it from occuring withing sleeping insulation. Might also depend on the surface area of tent being large enough to condense/remove moisture as fast as it is being produced.

Double wall obviously best to combine some ventillation with dead air insulating space.

Edited by livingontheroad on 10/08/2011 07:20:10 MDT.

I will post the same product information of the "Gear" forum but wanted to mention this here as being relevant to the subject.

I have been working with Joe at ZPacks to complete the design and make available the "CloudLiner VB".



The description from my TrailLite Designs site:

The CloudLiner-VB is a vapor barrier designed to be used as part of a winter sleep system. Made using ultra light non-breathable cuben the CloudLiner helps control moisture vapor from entering the insulation of a users UL quilt or sleeping bag.

Weight (size regular): 1.5 oz.

if i need a VBL i just carry a heatsheets bivy at 4 oz

the problem with a VBL is that is is uncomfortable for some at temperatures above freezing, though they still work

one thing to keep in mind is that once you add up all these goodies (double wall, vbl, overquilt, nalgenes, etc ...) or even use them individually ... you do have to ask yrself is it worth it and the fiddling than just to get a synth bag/quilt ...

and en-rated 20F cats meow or other equivalent bag costs $130 and weights 1200g .. thats 200g more than a helium at 1/2-1/3 the price ... and of course there are always the MLD quilts ...

not to say synth wont get damp, but you can usually dry off that dampness with body heat and a nalgene ... and you can wear your down jacket/pants inside (moves the dew point to the synth bag, rather than the down bag otherwise)

as the OP found out, synth can save yr azz if you make mistakes, or the weather gods eff you over

i think i hear a few kitty cats purring ;)

"one thing to keep in mind is that once you add up all these goodies (double wall, vbl, overquilt, nalgenes, etc ...) or even use them individually ..."

My complete winter shelter/sleep systems weighs less then most double wall shelters;

MLD cuben SoloMid = 9 oz (not counting stakes and hiking poles)
MLD event Soul Bivy = 12 oz
Nunatak epic arc Expedition = 34 oz
CloudLiner VB = 1.5 oz

Total = 56.5 oz (3 lbs 8.5 oz)

This is a storm worthy and effective solo UL winter shelter/sleep system for the conditions I hike in.

Edited by thomdarrah on 10/08/2011 10:46:50 MDT.

"This is a storm worthy and effective solo UL winter shelter/sleep system."

I would change that to "This is a storm worthy and effective solo UL winter shelter/sleep system for the conditions i hike in."

"But that might be preferable in calm conditions if it keeps it from occuring withing sleeping insulation."

I would agree with this Martin - especially with what I encountered.

"as the OP found out, synth can save yr azz if you make mistakes, or the weather gods eff you over"

True Dat!

Years ago I read several articles completed by Dr.J (Ryan Jordan) espousing the merits of synthetic insulation. Last weekend, synthetic insulation was a Godsend and kept me out of true hyperthermic conditions. Although the synthetic insulation did get a bit wet (evidenced by the massive internal condensation in my down quilt and bivy), I did not notice much of a drop off in warmth from the syntetic garments. The quilt and bivy were very, very wet in comparison.

Hi Mike,

Hope all is well.

Does your Warmlite have the liner or is is the single skin one?
Any idea of the temperature the night you had the really bad condensation?

Cheers,

Stephen

Awright Stephen. :)
I'm guessing maybe 5 or 6C.
It was a 2R. (double skin) The Stephensons tents create a warm micro-climate, so any dewpoint is going to be outside your sleeping gear.

Alright Mike :-)

5 to 6C sounds like a balmy Scottish Autumn ;-)

I am on the search for a Winter tent for when I move to the US at the moment (have an add posted for a Soulo) but I keep on coming back to the Warmlite.

Will have a closer look at them.

Cheers,

Stephen

So when is someone going to come out and just say Ure is a wuss?

; )

Hi Eric

> once you add up all these goodies (double wall, vbl, overquilt, nalgenes, etc ...) or
> even use them individually ... you do have to ask yrself is it worth it and the
> fiddling than just to get a synth bag/quilt ...
>not to say synth wont get damp, but you can usually dry off that dampness with body heat and a nalgene

I understand what you are saying, but I have to disagree with the idea that a synth quilt will solve it all. In fact, good down may resist wetting out better than synthetic insulation, as was shown in an article on jackets some time ago. But it gets more complex than that.

Yes, damp down does lose more insulation value than synthetic, but only if it gets to that damp state. If you can avoid that down is better, and good down can be hard to wet out.

Down can be dried off just as fast as synthetic in my experience.

That's just the start. Other wider factors come in. they include;

If you use a good double-skin tent under 'mild' conditions and can keep the inner tent just a little bit warmer than the outside, you may well manage to keep the dew line outside the inner tent. The slight temperature benefit of the inner tent can mean that all the moisture is trapped by the fly. The inner tent can then usually block any drips.

If you have two people inside a good double-skin tent you have a far better chance of managing the conditions as you have twice as much heat supply in an only slightly larger volume. I guess that having three people would be even better, although I have little experience there. Adding an all-night candle can also work by just adding a couple of degrees to the inside, as above.

Even in way sub-zero conditions when there is no chance of 'water' condensing because it goes straight to frost/ice, having two people close together seems to keep the frost line outside the quilt. Plenty of times I have scraped frost off the outside of our quilts without seeing much loss of loft on the down inside. That's over several nights.

One thing I will hold to though: you can't do multi-night trips in extreme conditions with the same UL gear you might use in the desert in summer! The definition of UL has to adjust to the conditions.

Cheers

I don't have this problem when I use one of my double wall (with inner mesh) tents.

So is a mesh inner enough to create a sufficient temp differential to shift the dew point?

Depends on how low your outer is to the ground, amount of breeze, and heat bodies on the inside.

There is no 'right' answer all the time- its just war between heat bodies VS wind/ humidity.

If its windy the heat will get blown out of the tent and the dew point will be inside the inner. That is, unless you have sufficient heat to overpower the wind.

True, wind will help with humidity, but at 100% humidity (ie. being in fog) its just a heat killer but stays moist.

i have never had down dry a fast as synthetic ... the closest was a damp exl, which still took longer to dry than my 170 gm primaloft belay jacket ... but thats just my experience

there are tricks to drying down, but then you can use the same tricks on synth to dry it even faster ...

synth is not a solution for everything, but IMO it does offer a greater margin of error ... now true BPLers shouldnt mess up of course ;)

but in humid environments close to freezing i personally dont want to be taking a chance with my sleeping system ... i know i can dry a damp (not soaked) synth sleeping bag with body heat and nagene and ill survive ...

there is a decent amount of threads of down quilts getting damp every year for it to be somewhat of a concern, not necessarily to use synths ... but enough for people to know the limits and skills ... some crazy old bums on this site use site use synth quilts, those weird alaska trekkers named RJ and AS ...

besides im a loner .... no spooning partners for me =(

Edited by bearbreeder on 10/08/2011 19:54:06 MDT.

Bearspooner? ;)

This has been a great discussion and I'm finding that Roger keeps explaining many of the things that I've observered but never really understood.

My observations are just that observations with no science behind them. I think we need a BPL research article on this topic to draw all this info together into something meaningful (Roger?).

Jason -

>> So is a mesh inner enough to create a sufficient temp differential to shift the dew point? <<

To answer your question regarding the mesh inner making all the difference, I would have to say "sort of...". The two double wall tents that I use for backpacking are the Fly Creek UL1 and the Copper Spur UL2. I've settled on these tents for exactly the reasons that Roger has explained above.

These two Big Agness tents have much higher (breathable) fabric inner walls than most tents and the mesh starts fairly high up on the sides. I have found this design blocks the breeze better than a full mesh inner which keeps the tent warmer and also traps the heat generated by my body better.

Even though the Fly Creek UL 2 is roomier and barely heavier than the Fly Creek UL1, I've stuck with the Fly Creek UL 1 because it is smaller and I would expect that it will be warmer with only one person in it (less area for my body to heat up).

The Copper Spur UL2 is a small tent for two people but I have recorded temps that are 5 degrees warmer inside the tent than it is outside, when two people are sleeping in the CS UL2.

Eric -

>> some crazy old bums on this site use site use synth quilts, those weird alaska trekkers named RJ and AS ... <<

I think there is a big difference in the equipment used for expedition long outings compared with the typical week or two long trips that most people will go on. I do think that repeatedly subjecting a down bag to damp conditions (for a month or two) will take it's toll on the bags ability to keep you warm.

I've never had a problem with my down bag in damp conditions but most of my trips are a week or less and with a double wall shelter. I actually find that my down bags seem to "breathe" better than a synthetic bag (my down bags seem to trap less condensation from within). If I'm expecting a lot of condensation on the outside of the bag (ie. single wall, high humitity, very cool/wet weather) then I would either use a synthetic bag or my WP/Breathable bag cover on my down bag.

Double wall shelters have their problems as well when things get brutally damp like David experienced. I've had my fly get so heavy from the rain outside and the condensation inside(and a bit of deflection by the wind) that the fly sticks to the mesh inner (basically a soggy mess). I've also found that my silnylon floor can be condensation prone (I still don't understand that one).

Edited by skopeo on 10/09/2011 01:45:39 MDT.