Cuben Summer Quilt

[Peter Nash]

Cuben mania caught up to me this year (I know it’s a little late, but now I’m all in). My backpack, shelter, and rain gear are newly acquired Cuben gear from Zpacks. I recently bought a beautiful Ephiphany 20 Cuben quilt from Enlightened Equipment, and owing to Tim Marshall’s excessive generosity I wound up with an Epiphany 30 also. These quilts persuaded me to never hike again with any quilt that isn’t Cuben.

Most of my hikes are in Michigan in late spring through early fall, so a higher temp-rated quilt would be a great addition to my Cuben collection.

I decided to make a Cuben quilt meeting these criteria:

1. Temp rating good to about 45 degrees F.
2. Designed specifically to be used with a Neoair Xlite Regular sleeping pad.
3. True vapor barrier: Cuben fiber without stitch holes in the insulated area (stitched side hems Ok, if outside of taped joint.)
4. Under 10 oz.

I have used vapor barriers in warmer weather for years, and they work fine for me. And as long as you can make a VB work, you will save weight over a comparable non-VB quilt.

Ten years ago I got a custom Nunatak Arc Alpinist with silnylon inner fabric, to act as a vapor barrier. That bag does have stitching in the silnylon though, so it will allow humid air to get into the insulation. A stitchless Cuben quilt would be superior.

My design was especially inspired by two other quilts made by Tim Marshall as specified by Steve Evans and Lynn Tramper. These BPL forum threads show those beauties:

http://tinyurl.com/l49zc2u

http://tinyurl.com/kxzyh26

My final design called for:

46” top width, 36” foot width , 71.5” length, with a rectangular foot box 14” wide by 11” high.

13 down chambers in the main quilt, 2 in the footbox, all spaced at 5.5.”

1.5” Cuben baffles, with two noseeum vents in each baffle to allow air flow throughout the down chambers.

The design called for a breathable fabric vent in each down chamber to allow the quilt to loft and be compressed. I chose Impetus 1.0 for this after Tim Marshall recommended it as one fabric that would work. I decided not to use a single “skunk stripe” because I wanted to have a single, unseamed piece of Cuben fabric for the quit top and bottom, and I did not want any stitches in any fabric containing down. The no stitches requirement meant that the baffles would be taped, as would the joining of the top and bottom of the quilt.

I added “wings” (like Lynn Tramper’s) to the quilt edges that can be tucked under the Xlite pad to block drafts. A tapered piece of Cuben extends across the sides of the quilt at the footbox to allow the Xlite pad to be secured to the foot end of the quilt.

I used .34 oz. Cuben and 5.5 oz. of 900 fill power down from Thru-Hiker. Finished weight came in at 9.85 oz.

I have spent two nights in the quilt, one in the upper 40’s, one in the upper 50’s. I slept fine. I did notice some water droplets inside the footbox after the first night, so the second night I wore VB socks (RBH), but I still noticed a slight bit of water there. Not a problem, but indeed an indication that the unstitched Cuben is a better VB than stitched silnylon.

Baffle vent close up:

Installing the top vents:

Joining top and bottom:

Quilt with Neoair pad inside footbox:

Finished Quilt:

Quilt in stuff sack:

[Daniel Saunders]

Nice work! Always impressed by the creativity here.

[Ryan Smith]

Very nice! Which tape did you use?

Ryan

[Peter Nash]

I got the tape from Cubic Tech. Their paperwork describes it as CTPSA-.5; .5" PSA. It's white transfer tape. You peel the backing off and stick the tape down where you need it, then peel a thinner 2nd backing off when you're ready to expose the adhesive. I have some brown tape from Zpacks that has only one backing.

[Colin Krusor]

Peter, did you sew the cuben baffles to the tape first, then apply the tape to the inner and outer shell layers? I have a MYOG cuben quilt also, but I chose to make the baffles from nanoseeum netting. I stitched the netting to cuben strips that I then bonded to the shell, so there are no stitches in the shell. This arrangement causes pulling forces from the baffle walls on the shell to occur along a line down the center of each bonded cuben strip, which minimizes the risk of peeling up the strips.

[Peter Nash]

Colin, I didn't sew the baffles to the tape. I folded the Cuben baffles to create a crease that I lined up with one edge of the adhesive. I pressed the baffles in place by hand, then finished applying pressure with a roller.

It never occurred to me to sew the baffles to the tape or to try your process. I used Cuben for the baffles because I figured it would be difficult to attach noseeum baffles without stitching. (Also becuse the Cuben is lighter than noseeum.) But your method is a clever way to use nosseum baffles without sewing into the Cuben quilt.

I'm don't think I understand what you're saying about the pulling forces, but I'm not an engineer. I can imagine that noseeum might have more give than Cuben; that it might stretch and absorb a pulling force better than Cuben. It seems like the taped Cuben will hold in this baffle application. I did some test Cuben baffles that I tried to pull apart and figured it would hold.

[Colin Krusor]

I don't doubt that your baffles will be plenty strong. In general, I just try to design seams and bonds so they have as much strength as possible because those are the places where things tend to fail.

All adhesives, and especially those that will bond low-energy surfaces like the mylar surface of cuben, have far more bond strength "in shear" than "in peel". It is hard to explain without a picture, and it helps even more for you to try it yourself. Imagine preparing two strips of cuben, each about 6" long and 1" wide. Imagine bonding them together with the tape so, from the side, they look like the image below (the tape is in blue). Once the tape has achieved full strength after several days, this bond will be strong if you try to pull the strips apart by holding points A and C, but much weaker if you try to pull them apart holding points A and B. When you pull apart points A and C, the bond is "in shear", and when you pull apart points A and B, the bond is "in peel".

Ideally, the seams in something made of cuben will be at least as strong as the material itself. This minimizes the risk of failures. This can easily be achieved in something made with 0.34 oz cuben if the seams are made well (clean surfaces, etc.) and they are designed to be "in shear". Seams designed so they are "in peel" will be far weaker, and will never approach the strength of the material itself.

It sounds like the above figure basically illustrates the way you made your baffle-to-shell bonds (piece A would be the baffle). No matter what kind of bond, any pulling on the baffle will result in "tenting" of the shell:

So, the forces pulling A and C apart are shear forces (not a problem for the bond), but the forces pulling A and B apart are peel forces (might peel apart the bond). If you add another piece of one-sided cuben tape (in green), then the forces are all in shear:

But this adds the weight of the one-sided tape, which, over something like 60 feet of baffle seams, will add considerably to the weight of the quilt. This was my reason for sewing the baffle material to a strip and bonding it. That arrangement is in shear, and it requires no extra material:

For some applications, a seam in peel can be adequately strong. As long as it appears to work, no problem. But accidents happen, things get caught on other things, yanked, etc. so my policy is to design all seams to be as strong as possible, if it doesn't cost anything more or add any weight.

Your quilt looks great, by the way. I like the little windows into each baffle, and the weight is excellent.

[Peter Nash]

Colin, thanks so much for your illustrated post. Now I get your point, I think. Your solution is to add a 2nd bond, to assure that both directions stressing the baffle seam are in shear, instead of a single bond that is in shear in one direction and in peel in the other?

Incidentally, I have followed your posts on the merits of using Hysol U-09LV instead of tape. I got some Hysol and did some tests. I believe that if done right it probably results in stronger bonds. I will play with it some more, and for shelter seams it seems like the way to go. But I figured it would take too long to finish my quilt using Hysol.

I do hope to make another quilt and any guidance you have is valuable.

[Hiking Malto]

If you used cuben on the outer for rain protect, ie under tarp, you may want to put a flap over the top vents. It wouldn't be bonded all the way around so it would function to get loft but it could provide 100% protection from rain or splash.

One additional thought. I have playing around with using VBL above freezing in combination with a lighter bag, basically what I understand you are doing. Please posts how this works for you especially the temperature range that it is effective, especially the upper limit.

[Peter Nash]

Hiking Malto,

The top is Cuben, the vents are Impetus 1.0 nylon. The Impetus has a DWR coating, and the vents cover only a small fraction of the quilt top. So, while adding flaps over the vents could offer protection against rain, I don't think there would be any benefit when used in a tent or tarp. A little condensation dripping on the vents should bead up and stay on the surface, and any amount getting into the down should be negligible, I think.

There is no upper temperature limit for Vapor Barriers, as long as you want some covering for warmth. That's what I've found. Many people don't like the idea of VB, fearing a clammy, sweaty experience. It may get humid or steamy, which can be alleviated by raising the quilt and letting fresh air in. I have used VBs for years in temps above freezing. The footbox will get some condensation from the insensible perspiration feet pump out. I can live with that.

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