Cuben sleep system

It's the Warbonnet Blackbird. A great backpacking hammock!

Update from last weekend: The night was around 40F, 5C, thick fog rolled in followed by rain. I slept very well mostly wrapped up fully, but when I got home and weighed the quilt, it had gained 41 grams/1.5oz. Most of the noticeable moisture was in the footbox region, so I think the fog was a minor contributor, but this quilt is definitely not waterproof in any meaningful way. I wish I had a normal quilt to compare it to RE: water weight gain…

Lynn, what kind of shelter system did you use?
Am I understanding you correctly that you think most of the water weight gain came from the rain (and not fog/your vapour)?

David

I was in a Double Rainbow, and I think a lot of the moisture came from my own perspiration, as the foot of the bag was the dampest part and that's where I tend to sweat most. But I think some of it was also from the heavy fog/mist that permeated everything. I just can't be sure. I wish I could do it again with a true VBL inside the bag to rule out body moisture.

"I wish I had a normal quilt to compare it to RE: water weight gain…"

Are you also weighing your down jacket (and pants if you have) before and after your trips? It's probably hard to compare, but maybe it gives a hint.

I used to always have lots of moisture around the foot of my quilts as well, even when I'd leave a 'hole'. So I started wearing VBL socks (RBH) and it took care of that problem. I always wear 'em now.

Doug, that's a sweet and cozy lookin' setup you have there.

Since you guys mentioned moisture buildup, I spent the night in my 15 degree bag, and the overnight temp got down to 28F. I was sitting up eating breakfast in my bag and noticed there was a lot of moisture around my waistline, where the bag was creased. So much that I thought I had spilled. Nope. It was just pushing out moisture from the bag and collecting on the shell. This has happened before as well. I don't wake up damp from sweat, but the bag sure as hell collects moisture, and this is my nemesis for winter camping.

"Are you also weighing your down jacket (and pants if you have) before and after your trips?"

It hasn't yet been cold enough for me to wear down, so no. But it's on my "to-do' list. Basically I had *hoped* that an all cuben bag would keep my down drier, and this has proved to be not the case. The stitch lines are permeable enough to let through a significant amount of moisture. I'm not disappointed though, as the system is still wonderfully light and warm.

Next trip I will try the VBL socks. Makes sense really.

Could the stitch lines not be seam sealed then?

when seam sealing all the stiches, the sleeping bag has no way to loft.
however, you could just seal the seams on the inner side, and leave those on the outer side open.

edit: i just saw that the bag is sewn through, so sealing one side only probably won't work.
but you could still seal the seams and then take a needle to punch a few (maybe more) holes on the outer side of the bag allow it to loft. if the needle is small enough, no down will escape.

No the seams are not sealed, and the seams are not sewn through (baffles are just under 2 inches). David is correct: If I seal the seams, the quilt won't loft/compress. If I seal the inner seams, lofting will be slowed, and I can still get wet from outer moisture, though this may be the best bet long term, as I always carry a 3 oz bivy that I could use if external moisture is likely to be an issue. However, when external moisture is fog/mist, even a bivy is little protection, so maybe I just have to put up with the occasional water weight gain??

Interesting. I hadn't considered the compression/lofting aspect but then again I'm new to the whole MYOG thing so I'm happy to learn. How about applying a DWR finish to the outer seams rather than sealing them entirely? That way any moisture which finds its way into the down could still escape as evaporation but no liquid water should be able to weasel its way in. Does that hold water (pun intended)?

These are the reasons that I had initial concerns about this design. I don't know what the baffle width is, so I don't know how many seams there are, but seam sealing would probably significantly increase the weight of the bag.

I think a completely bonded (no-sew) quilt/topbag with air-permeable (non-cuben) baffles and a small breathable patch on the outside furnished with a cover in the form of a cuben flap with a velcro closure, or some similar arrangement, would be much less prone to moisture problems. And, because such a design would be waterproof, there would be no net weight penalty from the breathable patch and bonded seams because it would obviate the need for a bivy.

Fabrication of a bonded quilt would be much more laborious and potentially problematic than sewing, though. I am planning to make a bonded cuben double quilt for my girlfriend and I but I found that my first design required 56, 7-foot-long bond lines. That design could be sewn in a weekend but bonding that many seams would take all summer.

Lynn, did the water gained from fog/perspiration evaporate pretty quickly? Did the bag return to its dry weight in a day or two?

The quilt dried out after sleeping with it at home for two nights. Body heat definitely does the trick.

I was gonna initially make a quilt exactly as you described, but worked out the extra weight of the bonding would make the quilt too heavy for my tastes. This quilt was a compromise, but knowing it's limitations will help me to keep the moisture out. In most cases I think just wearing bread bags on my feet will limit the water gain on colder nights. It's a non-problem on warmer nights.

Lynn, when you did the weight calculation for a bonded quilt, what bonding method were you considering?

I was thinking of doing a quilt using 1/4" hysol seams.

Hi Lynn

Why don't you try seam sealing the inside face only? That would keep your perspiration from getting into the down, and I do not think that any fog should penetrate from outside when the bag is always going to be a bit warmer than the surrounds.

Now, how to easily seam seal a stitch line in Cuban fabric? Easy! Ordinary sticky tape! Go on, try it. You can always pull the tape off later if you don't like it.

Cheers

I'll give it a try, at least in the footbox region to start with. I agree, I'm not worried about moisture penetrating from the outside, but I do worry about decreasing loft time if I seal too many seams.

Lynn,

Like Nia, I am a bit interested in how you estimated the weight of bonded seams. I'm not asking just to be contrary (although it seems to me that well-done cuben seams are not heavier than sewn seams), I am actually interested in how others are making their cuben seams and what kinds of estimates people are using to predict the weight.

I was looking at using cuben tape at around 3 grams per meter. Not sure how much other bonding methods would weigh?

Oh. Tape. I think tape is quite a bit heavier and less reliable than careful Hysol seams. Very thin, strong, almost invisible seams are possible with the low-viscosity Hysol (U-09lv). I don't think they weigh more than sewn seams (the layer of adhesive can be imperceptibly thin and they can be made with much less overlap than sewn seams).

Anyway, thanks for your reports on your new quilt. It seems perfectly serviceable and quite a bit lighter than any commercial equivalent. My compliments to you and Tim. I look forward to more field testing and updates.

Yeah, glue might well be lighter, but too hard and too much chance to screw up IMHO. It's a LOT of seams to bond, and I'm not even sure it would bond nano-see-um netting to cuben. I'm also walking a fine line of practicality in terms of weight. My previous sleep system was a WM POD30, which weighed in at 425g/15oz and included a hood. It kept me warm down to freezing. This cuben system is 12.7oz/360g for the quilt, plus 1.5oz/45g for the balaclava. Not really saving much weight in total, and turns out to not be very waterproof. Adding even a little extra glue weight would make it heavier than my previous system…

sorry i missed this thread until just now.

If you desire a completely waterproof inside surface you should choose the synthetic version of the quilt. There are no needle holes on the inside and the only way for water to enter from the outside are the obvious head and foot openings along with the stripe of 20D nylon which now runs across the chest.

I have experienced water weight gain in my breathable down bags in the past and as long as you are sweating you can expect some of that to get into the bag/quilt(unless you have the Epiphany XP). But i agree that if you leave the bag out to dry or just the act of sleeping in it will provide the needed heat to dry it out. If you are worried about water vapor getting trapped inside order the nylon stripe.

These quilts are for sure not for everyone, but i only know of one user who decided it wasn't for them after ordering one.

VB socks also make the experience much better as the footbox tends to heat up the most (ordering bigger foot width will help too)

-Tim

"If you desire a completely waterproof inside surface you should choose the synthetic version of the quilt."

Awwww, that's no fun, it won't be the *lightest* and most compressible then ;)
I mean, look at the rolled size of that little beauty! So small, so light, and good to below freezing…

VBL socks have definitely made a difference. I am very happy with my little sleep system.

i am testing another synthetic option that may be as light and compressible as down. I am not ready to offer it yet as my initial test results were unusable. I will be re-testing soon.

-Tim