Silnylon Tarp – Fabric Deformation & Seams

[Andrew I]

Hi all (first post here and all that …)

I’m getting some tarps made and at present we’re playing around with seams and fabrics. The two fabrics were going to be 20D silnylon (36gsm) and a heavier duty 40D silnylon (55gsm) from ExtremTextil in Germany. So I was sent some early seam samples and all the 40D silnylon did the following when stressed (pulled apart at the seam – not with massive force):

Seam type made no difference:

So the fabric never broke, but it stretched / deformed to a surprising degree and one would think would ultimately fail (under field conditions). I should add that neither had been seam sealed (but I doubt that would make that much of a difference?).

Questions:

1. Is this the fabric at fault?
2. Is this related to the fact that the stitches are too close to the seam (flat felled, lapped) edge?
3. Is the needle being used too large / blunt? (the person who sent them often works with heavier duty fabrics)

I think the thread used was Gutermann Mara 70 (I’ll confirm soon). Ultimately we’re going with Tera 80. The seams were rock solid, but the fabric at the seam was not.

Anyone have a clue what’s happening here, is the fabric sub-par?

Many thanks for any and all help,

P.

[Andrew I]

I should add that if I just pull the fabric (that is away from the seam) this doesn’t happen at all, so clearly it’s the puncturing of the fabric that is creating this weakness – but it seems extreme.

P.

[R]

Does the 20D fabric pass this test?

Do other commercial products pass this test?

How does this sitch length (stitches per inch) compare to seams that do pass this test?

Maybe you should find a manufacturer that is experienced with your materials and application/use case? If you’re paying for this, you shouldn’t have to trouble shoot it and tell your manufacturer how to do it right. Who knows what else they might get wrong?

[Roger Caffin]

Without actually handling the fabric it is hard to be quite sure. However, I suggest there are actually two faults here.

The first is that the fabric weave is a bit too loose for this application. Not all fabrics need a really tight weave, and a loose weave is much easier to make.

The second fault follows on from the first: the coating is a bit too light and is unable to hold the weave together. This is not the same thing as the Hydrostatic Head.

I don’t think the sewing has anything to do with the problem: it is all in the fabric.

A cynic might suggest that the manufacturer is trying to use a cheaper fabric for a task which requires a high-quality one – and possibly does not even understand where they have gone wrong. But how you will handle this legally is a problem. “Not fit for purpose’ might be the simplest approach.

Cheers

[Andrew I]

Many thanks to both of you for the quick replies. There’s no big deal here financially – as we’re just playing around with prototyping and testing the waters precisely to iron out these kind of issues. So no legal or heavy duty financial problems as we’re not committed to manufacturers and bulk fabric purchases etc …  It will be interesting to test the 20D silnylon which is coming soon.

“first is that the fabric weave is a bit too loose for this application” – very possibly – when I first tugged at it I felt it seemed overly stretchy (especially on the diagonal) and that would tally with what you’re saying.

I wandered if it was needle size / sharpness. But even so, as you say, you wouldn’t expect that kind of outcome under load.

Certificate: Complies with Oeko-Tex Standard 100 Class II and REACH
Tear strength (DIN EN ISO 13937-4): min. 17,8kg

It’s stated as double silicone coated and has a HH of 3500mm. I’m surprised because ExtremTextil have supplied very good stuff in the past. I’ll contact them and see what they say.

Interesting. I’ve worked with the company that made these small samples many times and they’ve done excellent work. I’ll chat with them tomorrow and get some feedback.

Thanks to both of you – really appreciated!

P.

[Andrew I]

Just a minor update – as the more info the better.
This is the thread and needle that was used:

Thread = Gutermann Mara70
Needle / Size:  Groz Beckert  No.10  NM 90-14 (brand new needle)

I’ll contact ExtremTextil and see what they have to say.

[James Marco]

Well, I am not sure I should chime in here. I could be wrong, so this is more of a guess.

1) As Roger says, this looks like a loose weave. I do not see this as a problem though. It also makes the fabric quite light.
2) The stress you show seems to be localizied in a single area. I have had a couple tarps look exactly like after being subjected to severe loading. But, it was only at the pole area where uneven stresses caused this “point” failure.
3) I don’t think the actual stretching has a lot to do with the seaming. I believe you have an incorrectly sewn joint and/or the actual threads used in the fabric were slipping apart. You would have to continue the stress-test until the two fabrics actually parted company to tell the difference. You might very well find a combination of slipping loose out of the joint on some threads, actual breakage on some threads, and threads that pulled apart within the yarns making up the weave. As Roger says, this is typical of a loose woven fabric. (I am ignoring seam sealing(SS) here. SS complicates the issue by gluing threads together and you have to consider bonding, elasticity of any glues, tear strength, etc.)

A) IFF it was an incorrectly sewn joint, you can examine the causes of failure.
A proper flat seam (too many names for a “french” seam) to join two fabrics is the same as interlocking your hands. Both seams will contribute to the strength of the joint.

Normally, the first thread will allow a small amount of slippage allowing the second thread to also engage, adding it’s strength. The end of the fabric is wrapped inside where it is held again by both threads allowing slight slipage between all the threads. I have found that the joint is actually stronger than the fabric and never fails there. However, I have seen some instructions on the web that simply fold one end in to a loop. They often miss stitching the end in (usually burried in the seam.) The stitching needs to be rather firm with a fair amount of tension on the thread. More than is required for a simple hem. And, the stitching us usually a bit finer, especially with dissimilar fabric thicknesses. If the joint is at all loose, the thinner fabric can unravel, pulling the threads out of the joint as you show in your pictures. It might just be a matter of more tension while sewing the seam…(Been there, done that. I had designed a jacket with heavy back/shoulder fabric -2.9oz nylon- and light sleeves and front -1.1oz nylon- and it failed similar to your seam failure at the sleeves…the thinner fabric pulled out of the joint.)
There are a couple fixes. Pay very close attention to your seams while sewing (a sort-of painstaking way to sew,) OR, roll the seam again before sewing. Locking the end of the fabric in the seam is the key it preventing unraveling. But, double rolling does introduce more stress in the joint and more seam allowances. This is of lesser importance, usually. Try rolling one of the undamaged portions of the seam samples and extra time and stitch it down tight. This will also tell you whether it was the seam or the fabric, so it is worth doing, anyway.

Or…

B) If the yarn in the thin fabric are simply pulling apart (very difficult to tell from your pictures) then the fabric is just too light for your intended use. Back to Roger’s statement. Even the 7D fabrics are light but usually tear, not unravel in the weave.

Again, I really doubt that and believe the seam had actually failed.
C) IFF the thicker fabric simply was not able to fold tight enough around the thinner making a proper joint, BOTH parts need to be involved in the joint for strength, a sharper needle night have helped a bit. The blunt needle could have simply fractured the yarns of the thinner fabric as it passed through the join causing strength problems by simple perforation damage of the lighter fabric. The pictures do support this to a degree, but the extreme unraveling is also a problem. Both, perhaps??

In any case, let us know what you find. Good Luck!

[Andrew I]

Hi James

2) The stress you show seems to be localizied in a single area.

No it fails in exactly the same way wherever the pull stress is applied (and this is not a major force either) I can just casually pull at it with less force than you’d get from a taut tarp in a gust of wind.

There is no seam failure as such – the fabric beyond (outside) the seam edge is failing.

This is a 40D fabric (55gsm) – so you could argue I shouldn’t be allowed to talk about it here ! Not exactly ultralight. The fabric is extremely strong – but as soon it’s stitched it’s compromised to a degree where I have to side with Roger and feel it’s not fit for purpose. What good is a fabric that fails when stitched?

It might just be a matter of more tension while sewing the seam…

We’ll play around with increased tension and see what effect that has.

If anyone’s got a view about the needle used, that would be interesting.

Thanks James for the detailed reply.

Andy

[James Marco]

“No it fails in exactly the same way wherever the pull stress is applied (and this is not a major force either) I can just casually pull at it with less force than you’d get from a taut tarp in a gust of wind.”

Well, the usual way to test is to do it by cutting so much width (inches, cm, mm, yards or meters,) attaching ALL the fabric on both sides evenly to a straight edge clamp, and, attaching it to a meter…increasing tension till it won’t increase, anymore, roughly speaking. Hard to say about a finger pull. When I dropped a largish branch on the tarp, I got a lot of stretching in the pole area, very close to what your picture showed…more of a “point” tension than a tension test.

As I mentioned, a blunt needle may be perforating the fabric (case C above.) Try a sharper needle with a higher tension. Also, thicker fabrics will tend to have greater radius bends. Soo, you may need two different measurements on the stitches: one for the thin side, one for the thick side.

[Roger Caffin]

Hi Andrew

I am not sure exactly what size needle you were using, but fwiiw, I use a Rasant 70 thread and a #60 needle (eg Metz) for my tents.

This is a thinner thread than many commercial companies use for such applications, but it has proven to be quite strong enough in the majority of cases in all my tents – with a proper seam of course. For really crucial seams I do go up to a Rasant 100, still with a #60 needle.

Why do commercial outfits use a thicker thread? I was told by a mfr that it was easier as it required less care. Yes, he knew it was overboard. It was all to do with production speed.

Most commercial mfrs use a thick needle than I do as well. Yes, it does make a bigger hole in the proofed fabric, but there is less chance of breaking the needle – especially with the heavier threads they are using. Anyhow, the holes are solved by telling the customer to ‘seal the seams’.

You will find that some texts say that a (Rasant) 70 thread, or a slightly thicker (Rasant) 100 thread, ‘requires’ a thicker needle. The reason they say that is a combination of several things. A larger needle is easier to thread for a start – but I have no trouble. Cheaper threads tend to have lumps along the length and the lumps can catch in the eye of the needle. The Rasant brand I use is not cheap, but the difference in cost for a tent is ridiculously small. Finally, in most commercial applications the size of the hole made by the needle simply does not matter – but it does in tents and packs.

Fwiiw: I spent 27 years associated with fibre and textile science.

Cheers

[Andrew I]

Roger, just FYI:

Thread (on samples) = Gutermann Mara 70
Needle / Size: Groz-Beckert #10 Nm 90/14 (brand new needle)

Original plan was to use Rasant 120 and Gutermann Tera 80 on attachment points and main seam.

Yes, I’ve read a good number of your posts and though I’ve just joined I’ve been a long time reader of the forums here.

Very interesting and helpful and much appreciated.

Cheers,
Andy

[Roger Caffin]

But ultimately it is the fabric which is simply unsuitable for this job.

Cheers

[Andrew I]

Yes, I’m sure you’re right. I’ve emailed ExtremTextil so I’ll suspend judgment until I hear what they have to say – before putting this thread to bed.

Cheers,
Andy

[Sam Farrington]

Andrew,
Must apologize because I posted a link to the 20D fabric on BPL recently in a thread seeking fabrics around 15D. The 20D fabric sold by ET is spec’d a hair above one oz/sq/yd, so something might well have been omitted during manufacture. I’m surprised that a company with such a good track record would sent you anything like this.

But I’m curious: At the outset you said they sent you “seam samples,” but later that you sewed the seams. Not sure if this is relevant, but would like to be clear about what you got vs what you created.

Most woven fabrics have selvage, which is the loose material on each side of the fabric roll, and it cannot be used. Your samples may have been taken too close to the selvage. Also, once fabric pieces are cut to desired shape, it is usual to fuse or hot melt the outside borders of seam allowance (the edge that will go into the seam) so that the fabric will not unravel. The can be done with a hot knife, but I just use a Bick lighter run down the raw edge. Having spent most of my life wandering in the backcountry, am not ashamed to be primitive.

Suspect that they did not melt the edges of the swatches they and/or you sewed into a lap felled seam. That coupled with taking the samples too close to or right along the selvage would create the result shown in your photos.

But it also may be that the fabric is defective, and was not treated with adhesive as it was woven. This would also create a like result. There was a great video posted here recently about how nylon fabric is woven.

Please let us know what they say to your inquiry. Thanks.

[Andrew I]

Hi Sam and thanks for the post.

To clarify – the fabric came from ET (let’s called them “supplier”), and was shipped to a company we’ve worked with many times (let’s call them “manufacturer”). The “manufacturer” sent me the seam samples.

1. The seam samples used the body fabric not the selvage
2. Hot melt – pretty sure cut with hot knife (I’ll check)
3. Yes – will update with whatever ET come back with (I’m very interested in their response – and I completely agree with you regarding their track record – I’ve ordered plenty from them in the past and have always been impressed with products and professionalism of service etc  …

Thanks again Sam.

[James Marco]

Sam, I don’t think the fabrics are glued together as they are woven. I don’t remember doing that, ‘corse that is from 45+ years ago. A billet may be calendared and/or coated after weaving. But, even humidity can be a pain in the butt by causing a lot of rethreading the weaving machines. (Broken threads get woven in causing a visible flaw in the fabric…often sold as seconds.)

Overpressing and/or “cold pressing” during calendaring can cause brittle, weak fabrics. But, this does not appear to be the problem. (This will show up as a tear along the joint, though, not an unraveling. Usually calendaring will embed the yarns within each other. Overpressing or cold pressing will actually cause the fibers to cut into each other making a rather “brittle” or “plasticy” fabric.) Roger can check me on this. I would say the opposite in this case, perhaps not even calendared, since the weave is simply pulling apart under stress.

I would cut a swatch and test the tension on the fabric. If this is good, then look to the sewing technique. A smaller, size 70-80 mictrotex sharp (RS or similar) will not cut fine fibers in a yarn. What may be happening is a size 90 round point is piercing the heavier fabric fine, but because the thinner fabric is wrapped both sides by the thicker, it cannot move. Soo, the blunt simply breaks through the fabric, rather than pushing the material around the needle. Anyway, good luck.

[Sam Farrington]

James,
The video I mentioned was posted by Franco and is at:
https://www.youtube.com/watch?v=YYWlevX7Kw0

It states that the glue is removed after weaving and when the fabric is washed before it is dyed. Not sure if calendering is involved, as Andrew’s material does not appear to be calendered.

I always sew with ball point needles to avoid cutting the material; but again, am not sure that is relevant to Andrew’s query, as it appears that the whole weave came apart, not just the threads at needle holes.  Hope he receives a response from Extrem Textil that is helpful.

The additional info that Andrew provided suggests sewing a lap felled seam with the ET fabric at home and seeing if  there is a different result when the seam is stressed.  That may be helpful before contacting ET.

[James Marco]

Sam, yeah, well it HAS been over 45 years since I ran a weaving machines(s) at Dufold. Anyway, it appears the glue is removed by washing it out, so, I am not sure what effect it has on the finished fabric.

Yes, I always used a ball point, myself. But I had some trouble with an old jacket similar to the pics. The only other place a narrow (“sharp”) needle was useful was with sewing a tent floor to a tent canopy. Anyway, I’m just guessing at this point…

[Ken M]

I think it would be interesting to “sew” a line (oriented as in original photos) WITHOUT thread, away from fabric edges and in only one layer of fabric..  Use thick, thin,ball and/or sharp needles.  Observe what is happening to the warp threads… Are they wedging the yards apart?  Or ripping yarns?  Then pull apart “on the dotted line” and see if it ruptures.

I suspect as others have noted, that the weft yarns aren’t wrapped tight enough to keep the warp threads from cleaving apart.  ie weak fabric.  Might have been a defective run of fabric?

[Andrew I]

Okay, so I’ve had a reply from the main guy (I’ll refer to as “M”, at ExtremTextil (ET) and it’s not quite what I expected, but it’s interesting. I’ve decided to quote it in full as it’s reasonably nuanced and I don’t want to misrepresent ET by quoting out of context.

The main takeaways for me are:

1. ET conducted similar localised pinch/pull tests and got similar results
2. Roger Caffin’s assessment of loose weave is correct
3. This looser weave was well understood by ET but was regarded (in real world stress testing) as a feature and not a bug (see below)

I asked M @ ET to look over this thread, quoting Roger’s initial assessment and stating thread / needle used and asked what he thought. Here’s M’s response (I’ve skipped the intro formalities):

The density of the used base fabric affects many technical properties. For Silnylon tent fabric the mainly important properties are tear resistance as well as stretch and touch. A tighter weave results in a lower tear resistance, in a stiffer touch (and hence louder in the wind, like spinnakers on sailing boats) and in less stretch (also a typical requirement for spinnakers). In contrary a looser weave results in a fabric with more tear resistance, softer touch and more stretch. The enhanced tear resistance makes the fabric more reliable when damaged and the softer touch prevents overly loud flapping in the wind. An advantage of the higher stretch is, that it makes the fabric more tolerable against tear based on uneven seams or faults in construction when sewing the tarp since the stress is distributed over a wider area. The latter is especially advantageous for less experienced sewers that either sew or lay out fabric in an uneven way or when pitching for instance a tarp with overly much stress in one point. The stretch helps to distribute the stress over a wider area and prevents the fabric or seam from failing.

Due to the above reasons we decided for this fabric as a versatile option for MYOG-projects (of course besides the highly reliable waterproofness). We of course made several sewing and in-field-tests in advance and of course we also took into account the seam-strength that the fabric can hold and made tests as you did. We also experienced that the seam could be pulled open when torn on a thumb-wide point as you did. But as soon as the tearing [** pull force ** – my edit] is farther away and on a bigger area the seam held the stretch since the load was distributed to a wider area. This also showed to be the case when the fabric was used in application as tarps or tents when tie out points were properly constructed and reinforced with extra layer(s) of fabric to prevent overly punctual stress.

So, based on the above points I would like to recommend that you review your testing method to evaluate the fabric. Of course seam construction and used needle and thread influence the stability of a seam but in my opinion it is not the decisive factor (I would recommend the Rasant 75 or Alterfil 80, a 80 Jeans or Microtex Needle and stitching width of 3mm). I still think this fabric is a good choice for tent and tarp applications. We’ve been selling this fabric for several years now and didn’t get any negative feedback from customers on the seam-strength or seam slippage. It only showed that many customers would prefer a fabric with less stretch so we are currently reviewing to add tent-materials with less stretch.

Nevertheless, the various properties of a fabric must be balanced out properly to make a suitable tent fabric. Past experiences unfortunately showed that fabric manufacturers don’t always manage to hold this balance. I will re-check the fabric that is currently on sale if there were any variations in seam-strength and seam-slippage. I will keep you updated on the results.

Here’s my reply:

Quick question: Does what you’ve written below also apply to the 20D silnylon?:
https://www.extremtextil.de/en/ripstop-nylon-tentfabric-silicone-coated-20den-36g-sqm.html

It seemed equally stretchy – but we’ve not yet had time to do the same seam tests.

There’s no problem for us as we use that same fabric (40D silnylon) in a number of other projects (and really like it) so no wastage.

I think what we’ll do is run a similar (but more even pull) test with the 20D fabric and see how that works out. Then we’ll make an actual prototype and see where we are. The company I use for such projects has decades of experience in the outdoor sector and so they definitely know what they’re doing. […]

Yes, I found the fabric to be very strong when pulled where no stitching had been done. So it seemed to me that the fabric was overly compromised by the stitch.

M confirmed that the 20D silnylon had similar properties.

Just to round this off, I informed M of the ad hoc nature of the test:

The “test” was done by me not the company making the seams and also they sent me the seam samples (not so much to test but just to show me which seams they could do for the tarp). So these seam samples weren’t that long and so a real world (controlled) test wasn’t possible — I just pulled at the seam to test it […] and was surprised at the stretch and deformation that occurred.

Hopefully that’s of interest.

Andy

[note: thanks to ET for granting permission to post their reply]

[James Marco]

Thank you for the update. That pretty much confirms my thoughts on the fabric.

[Roger Caffin]

Interesting, and thank you and ET for the feedback.

For the record, I will disagree a bit with some of M’s claims.

A tighter weave results in a lower tear resistance,
In the context of silnylon coated fabric, this is not really important. The silicone coating greatly increases the tear resistance of any fabric. (PU degrades the tear strength.) I am not aware of any reports of fabric failure in bad weather (except for UV-degraded tents on the South Col of Everest).

in a stiffer touch (and hence louder in the wind, like spinnakers on sailing boats)
I think this misrepresents reality. A ‘tougher’ touch I will accept, but one which gives more confidence perhaps. As for the spinnaker comment, spinnaker fabrics made lots of noise because of the polycarbonate coating they used. My tunnels have the stronger silnylon fabrics and do not make lots of noise – although one tunnel I made years ago from spinnaker fabric was noisy.

and in less stretch
Some stretch is good, but too much stretch is NOT.

At the end, it is YOUR call as to what you want.

Cheers

[Andrew I]

Roger

I think these are all fair points. I would only say that M is of course from Germany and though his English is better than most people in the UK, it’s still not his native tongue. Whether that makes any difference, I’m not sure – but where there is potential ambiguity in his response – a little semantic slack may be in order.

Only one way to find out and that is to make one of these bloody things. We’ll make a simple prototype with the 20D (36gsm) and see how it goes (I’ll take a spare shelter with me for sure, during testing).

Thanks,

Andy

[Sam Farrington]

Hi Andrew,
Alice said that things just got curiouser and curiouser.

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.

The response you got from ET sounded disappointing to me.  But don’t know the history of the transactions, so shouldn’t judge.  But from your photos I expected they would at a minimum just replace any fabric you ordered.  Looking back at the 1.16 oz/sq/yd, ET silnylon I sent to Richard Nisley in 2015, he tested it at 1406 mm HH initially, and 773 mm HH after simulating aging with cold water washing, which is well below the 1500 mm HH standard for waterproofing.  So regret suggesting it in a post on BPL. That material was weighed by Richard at 1.17 osy, so am not sure it is the same 20D silnylon that ET is selling now, and that is spec’d by them at 36 gm/sq/m (1.062 oz/sq/yd – please check my math.)

In any event, hope we will see some resolution.  Will not be surprised if Roger’s initial take was correct.

Note:  “Touch” sounds like something that Google translator would come up with instead of “Hand,” used in the USA, as in “soft hand,”  a reference to how soft and drapable a fabric is.  Here, “soft touch” has a number of other meanings.

[Sam Farrington]

Hi Roger,
Re: “The silicone coating greatly increases the tear resistance of any fabric. (PU degrades the tear strength.)”

Can you advise how you would apply that to nylon fabrics that are silicone coated on one side, and PU coated on the other; such as Rockywoods 7D, and the Sea to Summit Escapist 15D nylon tarp, both of which are coated in that way.

Thanks.

[Author]

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