Cuben fiber-sewn/taped versus bonded

"Drew, Yes, it starts as two sheets with a core of fibers. Through pressure and heat over and under the mesh, it becomes one piece, usually partially melting in to each other…a true mechanical bond. This is basically running in between the squares created by the woven fibers. The interstitial barrier is simply that area, creating the overall waterproof sheet. No adhesives are used."

– James, thanks for the clarification, that makes sense.

"However, I have also not read of any failures of sewn-then-taped cuben shelters. The sewn-then-taped ridgeline on my ZPacks tarp seems plenty strong. I have only read about issues with sewn-only cuben."

Does anyone have an idea how well taped-then-sewn compares to sewn-then-taped cuben?

For example, I have a shelter that I have considered seam sealing (it's all sewn) or seam taping using zpacks cuben tape. Would this strengthen the shelter at all?

The failures were in shear but 3M only tested T-peel since they said it paints a better picture of the adhesives bond strength. I have only warned about this issue because I saw the failures happen second hand and I think bonded gear makers are not being honest with customers and/or not doing adequately testing themselves. As there is no way in hell, now that I know what I know, would I ever trust my life to a bonded only cuben shelter during a winter trip where shelter could make the difference between coming home and not. In this scenario a sewn only shelter would be much better as the cold weather would not effect seams performance. And obviously it goes without saying, the best is a seam that is both bonded and sewn.

I'll take a bow to that.

James, what is this "interstitial barrier", and where did you learn that Cuben laminates are manufactured without adhesive?

My understanding is that the basic all-Dyneema Cuben laminate contains four parts: a non-woven grid of Dyneema fibers, two layers of polyester film, and glue (which is cured with heat and pressure).

I looked at those 3 links that James shared earlier. Unfortunately, i could not find very specific information about how cuben fiber is constructed as to whether James or Colin is more correct.

The closest i could find was this from HMG's site, "The "sandwich" is then melded together in a high-pressure autoclave."

Melded how, purely heat and pressure or heat and pressure + glue?

I do know that the UHMWPE fibers are plasma treated as to increase surface tension as to bond same better. Normally they are very slippery, and very little bonds to it.

I have made some gear from cuben fabric and I have seen several shelters after a month on the PCT. My conclusion is that cuben cannot be sewn or bonded. Since the seams are usually the high stress points, the little fibers will pull apart and the product falls apart. Cuben fabric is not woven. Weaving adds a lot of durability and strength. But it makes the fabric stretchy and sailors hate that. Cuben was developed for racing sails to have zero stretch and short lifetimes, often just one race. A few thousand little flexes like the wind on a tent, and all those random fibers come un-bonded. Normal seam sewing does not work at all because the stuff is so slippery, even using sailmakers seam tape does not stop the seams from slipping and pulling apart. The very strong flat-felled seam does not work either. I have some photos of failed seams if you are interested.

"My conclusion is that cuben cannot be sewn or bonded. Since the seams are usually the high stress points, the little fibers will pull apart and the product falls apart"

How would you qualify that claim? I don't have any data on this, but BPL users have reported many times that their sewn or bonded/taped cuben shelters are holding up fine, some of them for years.

Sure, given enough stress and time and they all will fail…but so does every piece of gear eventually.

I am not sure what your claim is.

To me the solution might be to bond larger surface areas with greater amounts of overlap. if making a 6ft tarp for instance I might overlap two 54″ wide pieces by 1.5 ft and bond that whole area together, then reinforce certain spots with seams.

Theoretical idea:
Bond it with an adhesive that seams won’t tear through after it cures, before it cures sew in your seams using a fibrous kind off thread with lots of stray fibers to get mired in the glue, then apply a heavy sealant to the outside threads and fabric to lock them down, allow all off that to cure together under a press for X hours

I have only read about this

I have heard Cuben wears out fairly quickly so have shifted to thinking about that silpoly that’s less than 1 osy

For Cuben, the adhesive in some tape allows the fabric to creep.  3M 9485 is supposed to not creep

Spinaker makers use tape plus sew it.  Sew through two layers and have tape on both sides.  Where the needle holes are it weakens the fabric, but going through two layers mitigates that.  The sewn seam will not creep.  The tape will provide the most strength.

I don’t have any technical background regarding materials but I’m sharing my personal experience with a MYOG Tipi I made a few years ago.  All my seams are bonded, there is not a single stitch in my whole shelter, even the Uretek Zipper was bonded.  After 5 years of extensive use (This is my primary 3 season shelter) I yet have to see any of the seams to come undone / fail.  My seams were very simple, just 1″ overlaps.  I used a combination of Cuben Tape from Zpacks for the panels (Joe told me it was 9485PC) and Loctite Hysol (U-09-FL) for the reinforcements / tie-outs.

I haven’t used this tent in very cold conditions.  Perhaps 20*F has been the lowest  (i.e early spring).

Here a picture of the tent on the field in early July of this year.  (Crazy to still see snow in July, but as you all know this was a very wet year in California Sierra)

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