Silnylon Tarp – Fabric Deformation & Seams

Oh you would ask, wouldn’t you Sam!
OK, primer for those who are not familiar with this.

When a fabric tears, individual threads break. This is why we have a ‘tear strength’. But the picture is more complex than a single thread at a time breaking. While one thread is reaching its breaking point, the thread ‘behind’ it is being highly stressed, and the next one is somewhat stressed, etc, so the tear strength is really counting on the strength of several threads.

A traditional PU coating on one side tends to lock the threads together and prevent the distribution of load across several threads. That means the tear strength is derived from little more than one thread at a time. This tear strength is less than for the bare fabric, where the stress gets spread around a bit.

A double-sided silicone coating is not really a ‘coating’: the whole weave gets impregnated right through from both sides. One could argue that what we call silnylon fabric is really a silicone membrane reinforced with a fabric. The result is that the silicone coating distributes the load across lots more threads than in a bare fabric, and the tear strength goes up significantly.

You might notice in this photo that the ‘ripstop’ threads do not seem to be doing very much. They aren’t, all they do is badly degrade the HH or waterproofness.

Now, what about a Si/PU fabric? My understanding is that normally this fabric first gets a single layer of silicone coating from one side only, then a layer of PU polymer is applied to the other side. The PU coating has two benefits: it is more waterproof than the silicone layer, and you can apply ordinary tapes to the PU side. Side note: these days the coating mills are using a thermoset PU rather than the older version of PU. The older version is never properly cured and gets sticky when stored for a while. The TPU coating does not get sticky. It’s much better.

While I was testing some sylnylon fabrics (for Sam no less!), I took some photos.

This was taken at 100 cm water head. The fabric does bulge, doesn’t it? You will see however that all the drops of water leaking through the fabric happen on the ripstop thread lines. The bulk of the fabric is still almost intact. Since the ripstop adds little or nothing to the strength of the fabric, and degrades the HH, you can see why I am campaigning against the use of the ripstop concept.

One other thing was visible during this fabric testing. The (different) fabric below was a silicone/PU one, and when pressure was applied to the silicone side I could SEE the threads wetting out. The silicone polymer is porous under pressure. But when I applied pressure from the PU side, there were no leaks, not even at 200 cm head (double the previous photo.) And the threads did not get wet.

So I have to admit that Si/PU coatings may be the way of the future for really high performance. And nylon fabrics do stretch nicely!

Cheers

Merci, Roger!  Very informative and helpful.
And here I always thought I sent you good stuff, which would easily hold water at a mere 1000mm HH. Or maybe that was the paraglider stuff which was incredibly light and strong, but not so waterproof, as you found.

Also note that the sil side of sil/PU coated fabric is not anywhere near as slippery as conventional silnylon, and the PU coat appears to be more elastic, hence less vulnerable to abrasion, especially if underneath the floor. So it may be a wash as to which side, the silcoated or the PU, should face out. Maybe PU on the outside of the outer canopy, which can get heavily drenched in rainy regions, but is more prone to abrasion at the bottom of the floor. For the floor and the rest, maybe a major consideration is that the PU side should go where one wishes to bond reinforcement patches for guylines and high stress areas. Unless one has your magic adhesive that bonds silcoat to silcoat.

It’s interesting from the first photo, that almost all the water drops penetrate on parallel lines of the ripstop grid, but not on the perpendicular lines. No idea why.
But with highly water resistant coatings, both gridlines should be protected. At least that’s been my observation of the ‘good stuff.’

Another observation is that ‘membrane’ polyesters without riptstop grids can rip under pressure right along the warp or weft if penetrated by a pinhole. A ripstop grid will retard that. So I think there is an argument to made for ripstop weaves, in tent as well as pack fabrics, and not just for their placebo effect. Of course, better nylon is less prone to rips, so maybe the arguments and counterarguments wash out on that subject also. It is a riddle, wrapped in an enigma, wrapped in … etc.

“It’s interesting from the first photo, that almost all the water drops penetrate on parallel lines of the ripstop grid, but not on the perpendicular lines. No idea why.”

Sam, I believe the silicone coatings are applied, in bulk, with rollers/scraping blades removing the excess. The thicker ripstop threads, being larger, stand up a bit more than the fabric, hence get a higher pressure removal of excess silicone, often too much. I believe this is what Roger’s picture shows. Thicker coatings cost more and are heavier. (One of the reasons I coat tarps/tents before using them.)

There is a fair overview of the types of machines used for this in this slide presentation:

It pretty much outlines the various coating processes.

James,
Thank you for the overview.
I do think that if coatings are mfg’d well, we will not have to add to them manually.
Making very light gear is a lot of work as it is, and do not want to spend even more time with remedying deficiencies in manufacturing materials. So use only the ‘good stuff,’ although will admit that ferreting out the wheat from the chaff can also be time consuming. Was just beginning my education in that process when sent Roger the leaky sample in the photo. More recently have been able to find better fabrics, also with the help of Richard Nisley.

Bottom line: I think the appeal of MYOG depends on finding materials that are already well manufactured and can be incorporated into gear either as is or with very simple modifications. Were it not for that, wouldn’t spend the time on MYOG, as there is more to life, including the actual hiking of course. Fully understand why most folks want quality gear that is ready made, and focus on the Gear, not the MYOG forum. But designing better gear can be very tempting, especially when it markedly improves the enjoyment of hiking. Sharing it on BPL can also be a lot of fun.

One exception to the above are better sprays that add DWR, and sometimes even some WP, to flies and apparel that need to be refreshed. Don’t mind that. but try to obtain materials with an effective lifespan so spraying does not become a habit, except on foot gear of course, which for me are definitely not MYOG. Not long after Goretex first came out, obtained same GTX fabric laminate and labored over designing and making an anorak that contained many features not available in the market. The GTX delaminated after one trek and the garment was worthless, but kept it as a reminder of a lesson learned.

DWR coatings are fine for apparel, though I don’t trust them. I have a North Face DWR jacket that simply leaked from day one. I tried several sprays with little help. Anyway, the “cutting edge” of new fabrics cuts both ways.

Roger makes an excellent argument for non-ripstop fabrics. Sam makes a good argument for durability. As always, this is the balance that will determine a good product.

Hi James,
Did not mean to imply that DWR sprays should be relied on for waterproofing. Sorry for giving that impression. Refreshing the DWR is helpful though to keep nylon fabrics from wetting out. A caveat though: Not all DWR sprays are equal, and a formulation that works for silcoated nylon, may not work for a WPB jacket. Once sprayed some DWR with silicone on some “waterproof” fabric and leather boots, and it turned the fabric into a sieve. Now know to read the label to check if GTX safe.

There are some sprays that may be for waterproofing: Penguin Ultra Dry Protecter, that states on the label that it “waterproofs” all fabrics; and Seam Grip brand Tent Sure, a McNett product, that states on the label, “waterproofs synthetic fabrics.”

Have not used either of these due to my expressed preference for coated fabrics with a reasonable waterproof life that won’t suddenly lose their WP after a total of a few months of use, as has happened in the past; and am not going to carry something like Tent Sure for the tent to keep functioning, at a considerably higher weight no less.
For the time and effort that goes into MYOG, I want something that will last, and keep its light weight and WP without the addition of heavy recoats.

Did use a Wilderness Equipment bug tent that was great in the rain because the fly provided a lot of awning coverage and could comfortably sit in the camp chair and prep and have dinner despite heavy rain:

. After a total of a few months use, the silcoated fly started to look a little ragged, but a DWR spray made it look like new. Don’t know if this actually restored the WP, but it made me feel more comfortable using the tent with no measurable weight gain. Later moved on to a lighter tent, from another company in Australia; but kind of miss the big awning, and am pondering how to design a lighter tent that still has that feature, and will also handle high winds.

My 2c.

Do NOT mix DWR with silicone spray. They are really incompatible. Putting either one on the other really trashes the lot, and it is extremely difficult to recover from it.

I do use a silicone spray to tart up the silicone coating on my silnylon tunnels. One application may last for about 2 years of use. But then, my blue tunnel has seen an awful lot of use.

Since the C8 DWR formulations were banned and the industry had to resort to C6 versions, DWRs have become not very effective. (C6/C8: the length of the hydrocarbon chain in the liquid.)

Cheers

Yeah, I don’t use sprays much…just a thin coat of brushed in mineral spirits/caulk. Anyway, getting back to Andrew’s problem… Sorry for pulling the thread adrift.

James, don’t worry about that (unless it was just a clumsy insert for a pun).

It’s all interesting info – and to be honest, there’s not a great deal to add re. the actual fabric until we make a prototype. I’ll update this thread when there’s anything substantive to add.

In the meantime, feel free to pull adrift.

Andy

From my post of May 3d on this thread:  “I will just order and sew some samples of the ET 20D into a lap felled seam, see if the seam (unsealed) unravels anything like what is shown in your photos, and will post the result on this thread.”

So a meter of the 20D silnylon was ordered from Extrem Textil on May 5th, and the charge for the fabric and delivery by registered mail was made to the credit card also on May 5th.  Received an email on May 6th that the order had been sent.  After several weeks inquired about the order, and the response was limited to providing a couple of tracking links: one in German that I do not read, and the other in English that suggested the order had been delivered in Minnesota, around a thousand miles distant from Chocorua.  (We went to my room-mate’s wedding in Minnesota by car, driving straight through by taking turns at the wheel, and it is for sure a long haul from the East Coast.)  Further inquiry has produced no response from ET.

Will probably have to let this one go, or ‘just write it off,’ as the saying goes; but am glad the lesson only cost $18.36 USD.  It is another cautionary tale supplementing Andrew’s experience, and is a shame, as there have been a number of purchases from Extrem Textil in the past that were prompt and quite satisfactory.  Life is for learning, as Joni Mitchell wrote.

Regret I’m not able to report to you as was hoped.  But the rest of this thread was very informative, definitely worth more than the $18.36.  And think I may understand Brexit a bit better now.

For some reason they have changed their tune, and will ship again at no added cost.
So maybe the mission can be accomplished. We will see.

Have there been any updates re the OP ? Im sitting here with a bag full of 20d from extrem textil that I intend to use for a tent im making.  I sat and sewed some test seams and when pulling at them got the same horrible pulling in the fabric as the OP.  Im concerned as to whether I should waste my time making a tent with this stuff?  Did you use the 20d for a tent? Did it turn out ok? Does seam sealing hold the fabric together and stop this issue? I was beginning to lose faith in my sewing but it seams ( no pun intended) we have the same issue?

Cheers

Paul

I sat and sewed some test seams and when pulling at them got the same horrible pulling in the fabric as the OP.
Some photos of the loaded seams would help.
But yes, some fabrics are woven too loosely to be useful in a tent (for instance).

Cheers

Paul,
I apologize for not yet following up as promised earlier on this thread.  Did send the Extrem Textil 20D silnylon fabric to Stephen Seeber just for HH tests, and he has posted his very positive results here on BPL.

So you have done what I intended to do. When cutting out the samples for Stephen, I noted that pieces cut near the selvage line (the line where the fully woven fabric deteriorates into partially woven, running along the edge of the roll) frayed very badly, even though the cut was on visually solid fabric. However, I noted that cuts made further away from the selvage line did not fray at all.

So what I plan to do now is cut out and sew pieces taken at varying distances from the selvage line to determine if there is a point away from the line where pieces can be sewn together with lap felled seams without the fabric unraveling when pressure is applied to pull the seams apart.

Your post now indicates that there are at least two different buyers for whom the fabric unraveled in a similar manner. This is quite discouraging, but I plan to go ahead when there is time because the Extrem Textil 20 denier silnylon fabric weighs 1.06 oz/sq/yd, or 0.02 oz less than a Sea to Summit Sil/PU nylon fabric that is 15D, should be stronger than the 15D; and perhaps more important, the 20D tested with a much higher HH than the 15D tested by Richard Nisley and also reported on BPL. The 15D showed an ample HH after simulated aging, but nothing like the 20D (over 6000 mm HH).

Would be interested to know how close to the selvage line you cut the pieces for your test. Like you, I want to be sure of the fabric’s properties before proceeding with the next shelter project. Hope that there is time to follow up this winter (in he US). Along with everything else am trying to house break a puppy right now and it is proving difficult. Suppose you could call that, ‘the puppy excuse.’

P.S. Would not depend on seam sealing to hold together an inherently deficient fabric. If the weave is that loose throughout the fabric, one could just stick a pin into it at any point and pull the weave apart. The 15D fabric was harvested from a Sea to Summit Escapist tarp, and should be quite dependable, if not so highly waterproof as the 20D from Extrem Textil.

Hi all,

Sorry about the delay in getting back to you all on this. I’ll provide some pics soon (just really busy at present).

Okay, so here’s the preliminary findings regarding this stuff. I did quite a bit of work with our (small) manufacturers. We believe for a robust tarp, using the loose weave 20D sil-nylon from ExtremTextil, there certainly seems to be a need to reinforce the seam.

Our approach for our first test prototype was as follows:

As you all know, basting tape is double sided adhesive tape. So we used one of those sides to stick a narrow strip (wide enough to accommodate all the double row of stitching) of spinnaker repair tape with the adhesive side up. So, in essence we customised our own re-inforced basting tape. This was then set inside a “french” (I think) seam. Stitched and then silicone coated on both sides.

I then tested the tarp in some very extreme (mountain top wind and deluge rain) conditions. It help up well, much to my surprise (I took a spare trusted tarp with me in case) over the 10 day trek. Too early to give any final proclamations — but that was our approach.

I’ll be testing it this winter (to see how it handles snow and cold) as a porch tarp with a hooped bivvy.

Would I recommend the fabric to MYOG types. It’s quite a lot of work and fortunately I’ve got some excellent outdoor industry people working with me.

Where ET may have a point is that I agree that the stresses did seem to get distributed due to the weave. There were times when I was sure the whole thing was going to get shredded or blow away (on one peak, I think I dreamt it had, and when I woke was certain it had been blown away in the storm) — but everything was still there. So it got a real thrashing and held up.

I think for a lightweight summer tarp the fabric has possibilities, but anyone working with it needs to find a way to reinforce the seam (I’m pretty sure of that).

Will update soon with pics. Sorry for taking so long.

Andy

As far as tents go – IMO the HH is too low for a tent. ~2000mm (may be a fraction less).
For me 2000mm is okay for a tarp – but I wouldn’t use this fabric for a tent.

During the test, there was one night (and this happened only once) which was very strange.
Some of the heaviest rain I’ve ever encountered (sounded like a firing squad shooting rubber bullets at the tarp). I could feel moisture but couldn’t work out where it was coming from. It wasn’t rain drops or anything like a leak.

It felt like someone lightly spraying an ultra-fine atomised mist.  The only thing I could think of, and this sounds crazy — but here goes, is that the rain was hitting the tarp at such a velocity that it was basically being shredded into fine particles by the weave of the fabric and on the inside of the tarp, hanging in the air like a fine mist. — Is that even possible for sil-nylon (loose weave or not).

It had no effect on all my gear (everything stayed dry). But it was very strange. I should emphasize that the rain was intense and this only happened once.

Andy

“It had no effect on all my gear (everything stayed dry). But it was very strange. I should emphasize that the rain was intense and this only happened once.”

Andy,  I have experienced this several times in the ADK’s. Even heavy duty tarps (like Cordura 1.9oz) do this. It seems to be a pressure leakage as you surmise. I started recoating my tarps because I thought they needed it and it stopped.

Several things influence this.
1) Stretching: All fabrics stretch to some degree. (Not including DCF here, though a case can be made for that, too.) Woven fabrics generally have warp and weft set to different tensions, mostly to facilitate the weaving process. One thread is bent more than the other as it weaves. But stretching can occur along the other. Usually calendaring is used to pretty much even out the threads, but if done at a low heat/pressure, it only minimally helps (mostly allowing a fabric to lay flat.) Heavier calendaring with nylons, poly, rayons and other synthetics, allows the fabric to melt slightly together bonding them in place, leaving only a little difference between the warp and weft stretching, but precludes any ripstop threads and imparts a “plasic” feel to the fabric. Any coating, such as silicone, can often break between the threads under stress in the first case. This interstitial breakage can be exacerbated by impact pressure from raindrops, especially in the heavy downpours you describe: Large, heavy raindrops. Once the coating is broken, it will ALWAYS be broken. In the second case, the fabric acts much like a plastic, scratch it and that is where it will tear. Neither case is good for tarps or tents.
2) I agree that 2000mmhead is NOT enough for tents and tarps (at least here in the ADKs.) I picked up 100yd of some cheaper silnylon that was rated at 2000 and in every tarp I made, they always “misted”, as you describe, here in the ADKs. They always required recoating. I switched to a somewhat heavier fabric (1.5oz) and I could use it the first year though rated only slightly better at 2500, I believe.
3) Recoating with a softer sealant before using it seemed to do the trick, for me. Stretch out your tarp as if you were using it, tensioning it tightly. Then recoat it with a mix of 30-50:1 mineral spirits/100% silicone caulk on both sides. Brushed in rather thoroughly, these tarps have lasted for many years with no further fussing. The downside is it adds some weight (around .2oz/yd.) And they become air tight. Care needs to be taken to NEVER trap air in them (or water if you are packing up wet.)

By the way am I reading Sam right when he says the HH test of the ExtremTextil 20D sil-nylon came out at 6000mm?  They quote much lower.

” nothing like the 20D (over 6000 mm HH).”

Andy

I’ve experienced that before

Heavy rain – misting inside but not enough to get anything wet, barely perceptible

Maybe knocking condensation off the inside

Maybe high pressure water (raindrops) through tiny holes in the fabric

Regular silnylon – I forget which one

@Jerry

Yes, thought it was the former when it was happening, then realised it wouldn’t cause the mist effect (would have been more droplets being knocked off the inside). Pretty sure it was the latter: “maybe high pressure water (raindrops) through tiny holes in the fabric”.

Andy

yeah, same here, I think it’s the tiny holes

when it happens I try to figure out which, but there’s no noticeable condensation

I have seen very fine condensation being knocked off the inside of the fly a few times. And yes, it was very fine water drops, not big ones. Also had it once with fairly dry hail.

I have never seen raindrops pushing water through a silicone-treated fabric, but that is just absence of evidence (not evidence of absence). The idea that it could happen with a very light loose weave – possible. I would need to test it at pressure.

Cheers

Andy, and all,
Stephen Seeber’s test result thread is recent, and posted on the Gear Forum, as Richard used to do with HH test results.

I get you are really busy, being so myself. ‘Misting’ silnylon has been reported and debated on this site since the forums began years ago. There was so much sub par silnylon being sold in the past that it could be expected. James’ theory is interesting. The reasons for leakage in any form can be very complex. The first material used by BD for its WPB tents was “Epic Malibu,” a yellow ripstop polyester with the Epic treatment. Some said it leaked, some did not. I held a high pressure hose nozzle right up against a sample stretched in a plastic embroidery loop, and neither a drop nor any mist passed through. But when Roger Caffin tested the fabric, he found that it resisted water penetration up to around 1500mm HH, but above that, came through copiously.

Mention this to preface an approach simpler than theorizing. I just put a brick in an empty bait bucket, stretched and tightly secured the Epic Malibu over the top, and left it on an uncovered deck during a fall when we had numerous pounding rains – there was major road damage also – the road up to Pinkham Notch tore apart, leaving a canyon that was not repaired for some time. As expected, there was several cm of water in the bottom of the bucket after several weeks.

There is plenty of the ET 20D RS left on the sample I bought, and will cut off a strip a few inches wide, running from the selvage line into the center of the roll. First, will cut off smaller strips from the big strip, beginning at the selvage end, to see if and when I get to a point where the cut edge does not unravel. If there is such a point, and it leaves a usable amount of fabric, will sew two pieces of the rest of the larger strip together with a lap felled seam, and see how it behaves. If not, will not use this fabric despite Stephen’s HH test.

Should note here that the ET 20D looks nothing like conventional silnylon. It appears to be sil, because dried Seam Grip peels off it on both sides. But there is no visible clear coat as with many silnylons.

Roger, I can send you a foot square swatch to test if you post an OK on this thread. The result would be interesting in view of Stephen’s rather remarkable HH test results.

In any event, am not reassured. The 15D with a sil/PU coat is starting to look better and better. Stay tuned.

Hi Sam

a foot square swatch to test if you post an OK on this thread.
Yeah, sure. Ah … ‘OK’. :)
That ET 20D sounds interesting anyhow.

I am rebuilding my Suter Tester to be more functional. Neat and compact. Should be a good test.

Cheers
Roger

Roger, OK, tomorrow is predicted to rain, so should have plenty of time to prepare and get a sample to the post office.  Any fraying edges will be heat sealed.  Any intact edges will be left as is.

Thought your Suter tester was pretty nifty as it was, operating something like a cider press; biut no doubt you have come up with some great improvements.