HH Test of Rip Stop by the Roll 15D Membrane Silpoly

Hi Stephen,

Thank you for testing the membrane silpoly that RBTR is currently selling.  Was hoping to use it for just a portion of a tent canopy, so am glad you saved me from wasting the effort.

The older samples of membrane PU2000, and PU4000 silpoly no doubt showed more HH, because they have PU coatings on one side.  Just as RBTR’s 20D silpoly with a PU4000 coat has HH tested much higher than the 20D without the PU coat.  However, the HH tests of the latter are completely acceptable, and it is much lighter, around 1.24 osy.  I also noted on my own that the older PU coated membrane fabrics came apart with just the poke of a pin.  So I think the message here is that 20D is as low as one can safely go if using silpoly for a tent.  Although adding a miniripstop might make the membrane more durable, there is no reason to believe it would provide water resistance at an acceptable level.

This does not come as a surprise.  When Dan Durston first posted about his 20D silpoly X-Mid, I commended him for resisting the temptation to use a lighter denier, what with all the rage for lighter fabrics.  But thanks to you, it is even clearer that the RBTR 1.1 oz (unfinished) 1.24 oz silpoly is the way to go, even though it adds around 0.2 oz/sq/yd to a tent.  (The current membrane weighs in around 1.04 osy with coating.)  That comes to about a total of 1.4 oz added to a tent using 7 yd2 of fabric, which is not a deal breaker. and IMO is worth the benefits of using silpoly instead of silnylon.

There are a lot of pitfalls in MYOG for those who put an inordinate amount of time into tent making; so your help is very much appreciated.

How many samples were tested ( I reread, and saw you tested 5, sorry:) ) 100cm2 is a very small section of fabric, and if this is due to mfr defects, then maybe this is an issue with a particular lot of fabric. Also, I’d be interested to see if your previous results from the PU2000/PU4000 were repeatable on your new lab setup, just to make sure nothing funky is going on from one piece of equipment to the next.  Let not all throw the baby out with the bath water here. If there was no evidence of some sort of defect, I might be a little more hesitant to use the material.

Also, the current membrane silpoly is .93 osy finished weight per spec (I however assume you have measured your lot, Sam, to come up with the 1.04osy you stated) and it is indeed silpoly, not silnylon; I assume this was just a mistake in typing.

I don’t think there is inherently anything wrong with 15D unless it is the reason for the mfr defects. I’d like to see more samples from a different lot/color tested – I am more than willing to send a sample from my fabric if you are willing to test it, Stephen, thanks for having a look at this.

Hi Michael:

I share your concerns and am happy to test additional samples.

The samples that I received came in the form of 2 10″ strips that ran across the entire roll.  One strip immediately when through a wash/dry cycle to simulate aging.  The other was tested as received.    5 tests were done on the non aged strip.  Two tests were done on the aged strip.  I stopped testing on the aged strip be cause it demonstrated that aging occurred and tended to confirm the results from the first series of tests.

Of course, I share your concern about test accuracy.  At this point, the only likely area of malfunction are the digital gauges used to measure air pressure.  I use two gauges simultaneously and they were in agreement.    When I got such a low reading, I ran a test on a brand new WBP fabric.  I pressured it up to 20,000 mmwc, at which point I stopped the test.  I then tested the other two samples described above, which performed sort of as expected, although I would have expected the PU 4000 to do substantially better than the PU 2000.  Unfortunately, I could only get one reading on each of those.

The issue to me is not whether 15D in general is appropriate for the use intended by Sam.  I don’t know whether it is or not.   It is whether the industry can exercise adequate quality control to deliver what its specifications claim.    This is what Sam said: There are a lot of pitfalls in MYOG for those who put an inordinate amount of time into tent making.  The MYOGers and small shops should be able to trust they are getting the performance they expect based on dependable specifications.   If your samples do well, we have confirmed there is probably a quality control issue.  If so, how can Sam know that the lot he purchases will do what it is supposed to?

I will PM you and I will test what you send.

Thank you for these results! I agree with all the above comments about usability of the membrane silpoly.

Stephen, could you comment on these results versus the ones you looked at on a previous occasion? https://www.dropbox.com/s/yla4o5ab7x6i2ts/

Is this due to the rebuilt HH tester giving more accurate results or perhaps due to this current fabric sample having manufacturing errors and QC inconsistency compared with the previous samples tested?

Thanks Stephen, I’ll get you some fabric sent out this week!

Stephen, I ordered a yard each of the Membrane silpoly, silpoly PU4000, and the newest .77osy MTN silnylon 6.6 for testing, order # in your PM. RBTR has been a little slow shipping out since Black Friday (for me at least), so I’d expect delivery to get to you in the next two weeks. I am sure some folks on here would also like to see how the MTN silnylon 6.6 does. I am planning to use it on a small tarp primarily for the tear strength it has over the poly, so I’m less concerned about the HH unless it is like zero :). Let me know if you need anything else.

Looking forward to results.

 If your samples do well, we have confirmed there is probably a quality control issue.  If so, how can Sam know that the lot he purchases will do what it is supposed to?

Regarding this question, I think it is appropriate to note that the nature of this type of testing will result in the exploitation of a few defects (as you have pointed out) ruining the test. That is to say, pressurization on a 100cm2 sample will naturally find the “leak” i.e. defect, and the pressurization will then rip that leak wide open, when in fact this is not ever how a fabric would fail in real life use for us. We are not (typically) using this fabric to hold pressurized water – it might be argued that if you are making a dry bag for packrafting, ok, then this test method may be more indicative of real world use, but for me and most people building tarps, this type of test is not really telling us anything about how the fabric will perform for us in our products. Rain is not going to exploit the few defects that you have observed and cause the fabric to rip open at that point (I assume that is what was happening when you recorded your pressure readings). Sorry for the long post. I am as eager to see how the fabrics perform as the rest of us building shelters and other MYOG backpacking equipment, but we should all try to understand how the standards used to measure the performance of our materials relate back to real-world use. Hopefully this understanding will result in more and more relatable testing compared to real world use.

Michael, you’ve presented another argument for why some kind of dynamic test that better replicates wind-driven hard rain would be nice to have. Others have previously pointed out that a static wall of water/continuous pressure will tend to make the size of the weave interstices look worse than they really are. Yarn defects, as Stephen has shown here, could be seen as analogous to large interstices.

But Suter testing does tell us lots of things about fabrics tested. In this case, it appears (for now) that the weaknesses/defects of 15d Membrane fabric are obscured by PU coatings.

Being able to seal seems with tape is usually given as the reason why many tent companies prefer PU-coated fabrics. One can’t help but wonder if PU coatings also allow them to use cheaper fabrics as well. If so, this is a lose, lose for the consumer: the inferior fabrics might have poor tear strength to begin with, and then the PU coatings weaken that further. Maybe I’m coming to incorrect conclusions, but the high-HH sil/sil fabrics being used by companies like Tarptent and MLD (and sold by RBTR in their MTN line) really look like high quality coated fabrics in comparison.

I would be inclined to agree with you about the use of a PU as the base for the coating being a source of additional weakness (tear strength), but all the RBTR fabrics containing a sil-coat appear to be coated with a sil/PU blend on both sides. All of the products with the exception of the MTN silnylon mention sil/PU in their spec. Nobody seems to be complaining about the standard RBTR silpoly being an inferior product as a result of the sil/PU coating on both sides. None of these are useful for seam-taping, the exception being those which call out the PU4000 coating on one side (various hex 2.2 , hyperD 300, and the SilPoly PU4000 fabrics come to mind). I’ve inquired with RBTR about whether there might be a difference. I suspect they do not source from only one mfr, so I doubt they will be able to provide a good answer. I just know that if they spec a performance number on their site, it should be good.

I am sure the Suter testing tell us useful things about the fabric when making comparisons between the relative qualities of competing fabrics. As for whether “it appears (for now) that the weaknesses/defects of 15d Membrane fabric are obscured by PU coatings” is a correct assessment/conclusion, I couldn’t be sure. I am also not sure that even can tell us whether a fabric is going to meet our performance requirements. It’s like EN temp ratings – for some people, a 30deg bag/pad is going to work for them at 30deg, for some it won’t, but the standard testing will help a person assess where to go from where they have started if they are still looking for a solution.

To clear up any confusion, I do not find any 15D membrane silpoly currently being offered by RBTR with PU2000 or PU4000 coatings.   Of those, what I have was purchased from RBTR several years ago, and sent some samples to Stephen only because he wanted to take a look at them.

What might be interesting for others, is that I did not have to cut off  Stephen’s samples of the PU2000 & 4000.  Just pulled and the fabrics came right apart on either the warp or the weft.  Even if the PU coatings do add to the HH,  I think that those PU coated membrane fabrics are much too fragile to use for a backpacking tent.

About the coating on the current 15D membrane silpoly, RBTR says it includes both sil and PU, and found one mention of it being a “blend” of sil and PU.  Regardless, it is not a separate PU coating on one side of the fabric as is the case with RBTR 20D PU4000.  Nor do I expect RBTR to share its proprietary formula for blends of PU & Sil.

While PU 4000 may add to HH, Stephen’s earlier posted tests found a high HH on the 20D silpoly “impregnated” with the “blend”, which met my needs even after simulated aging.  And with the above experiences with the 15D membrane silpoly PU 2000 and PU4000 fabrics in mind, I’m concerned that the PU coatings not only add weight; but also detract from durability.

So although disappointed with the membrane silpoly, I intend to go ahead with the more robust 20D RBTR fabrics and thus forgo many past experiences with sodden silnylon tents.

Stephen has corresponded with me a number of times about the efforts he has made to achieve reliable testing of the water resistance of backpacking fabrics, and I think we are very fortunate to have someone currently available and willing to do this.

Thinking on it a little more, I think Sutter testing is an excellent test for coated fabrics, mainly for “ruling in” fabrics that will perform adequately. We know from years of member reports and subsequent testing that if a fabric can hold a water column of >2000mm or so after aging that it will be worth the time and effort to use in a MYOG shelter. So Sutter testing is sufficient to establish suitability.

What we don’t know is whether we can assume that passing a Sutter test in this way is necessary to establish suitability. So this 15D Membrane has “failed” the test, but there remains some doubt whether it will fail in the field. So we might not be able to use the test to “rule out” a fabric with certainty.

However, Sam has used Stephen’s result to rule out this particular fabric for his use, and that seems wise. Yeah, it may be OK in the field, it may not, but why risk it for an ounce or whatever?

About RBTR’s blended sil/PU coatings, they say that you can use silicone adhesives on these fabrics, so silicone must dominate the mix. I don’t think I’ve read a good explanation for why they are mixing PU with silicone, or whether such mixes result in weaker fabrics than “pure” silicone coatings.

Interesting results. Thanks for this.

“I think the message here is that 20D is as low as one can safely go if using silpoly for a tent.”
I think the best explanation for the low HH observed here is the visible manufacturing issues  (e.g. twisted strands and gaps). I’m not sure that has anything to do with poly though, as I’m not aware of any reason why poly would be harder to weave than nylon. Maybe it is, but it seems more likely to be the result of quality issues, potentially exacerbated by thinner coatings (to save weight) which struggle to bridge those issues.

When Richard Nisley tested our 20D poly he noted the weave was ‘of high quality’ and his micrographs (which I shared at the time) were free of the quality issues shown here. He got an HH result above his testing maximum of 3500mm. I expect a similar quality weave and HH would be possible with a 10-15D poly from a high end mill but that’s just a guess – I haven’t looked into 10-15D poly primarily because I think 20D is the sweet spot for a well rounded fabric.

Even if a 10-15D was reliably waterproof, the durability of it would be pushing the edge quite a bit. I’d consider it on a niche/super light product but not on a more mainstream product designed for a long service life in challenging environments.

“Being able to seal seems with tape is usually given as the reason why many tent companies prefer PU-coated fabrics. One can’t help but wonder if PU coatings also allow them to use cheaper fabrics as well. If so, this is a lose, lose for the consumer: the inferior fabrics might have poor tear strength to begin with, and then the PU coatings weaken that further. Maybe I’m coming to incorrect conclusions, but the high-HH sil/sil fabrics being used by companies like Tarptent and MLD (and sold by RBTR in their MTN line) really look like high quality coated fabrics in comparison…”
I caution you about this theory (that companies are using PU to shave costs to the determent of the product). Companies do cut costs in many ways, but it’s also easy to make the argument “they’re secretly cutting costs” for almost any topic and thus lose sight of more the more interesting variables involved. And I don’t think this theory has merit here because it’s probably not lower cost.

Seam taping is really expensive and frankly hard to justify as a tent company because it adds a lot of cost AND makes the tent look heavier next to competitors that don’t seam tape (e.g. when people compare tents online they rarely factor in the cost/weight of user seam sealing). IMO, a much larger temptation is to skip the seam taping to cut $10 or so in costs off the product, and also be able to boast a lighter weight spec. But seam taping is better than user seam sealing IMO (more professional, more reliable) and saves the user cost and hassle, which is why we do it.

I don’t know the costs each company bears, but as far as I can tell the cost of seam taping is much more substantial than the cost difference between sil/sil and sil/PU. Sometimes it seems that sil/sil is more expensive, but other times using two different coatings costs more because with different coatings it becomes very sensitive how deeply you impregnate them (so they don’t interfere with each other). Even if sil/sil does cost more, I can’t see anyone saving an appealing amount of money by opting for sil/PU and then paying an extra $10 or so to seam tape. Maybe you could save money with a sil/PU AND not seam taping, but mostly because of the no seam taping.

Sil/sil has historically been a good way to go because it’s strong and durable (doesn’t degrade) but with the caveats that it can’t be seam taped (aside from Roger’s exotic method) and can make a floor awkwardly slippery. There’s a good argument to be made for sil/sil over sil/PU when the PU is traditional PU that does cost a lot of strength and does degrade (hydrolysis) over time. But modern PU coatings (aka PEU or PE) are way better than traditional PU in both counts. They largely eliminate hydrolysis and they can actually increase tear strength like sil does. Perhaps not quite as much as sil, but you can get very close in tear strength and equal in other metrics (abrasion, puncturing) while being non-slippery and able to seam tape. That the reason we use sil/PEU + seam tape, and I expect the same is true for companies like Gossamer Gear that do the same.

I’d sum it up like this:
– If a company is using sil + traditional PU and not seam taping, they are quite likely just cutting costs.
– If a company is using sil/sil and not seam taping, they might be cutting costs but may also (1) be doing it for an advantage in tear strength, or (2) previously had an advantage in tear strength in years past before newer PEUs came out and haven’t switched because switching fabrics is a major hassle/risk and if they’re a smaller shop they don’t have the machine to seam tape anyways.
– If a company is using sil/PEU (modern PU) and seam taping, they likely have the highest costs and are likely choosing these materials for performance/user friendliness reasons (good tear strength, able to seam tape, non-slip, good longevity).

I agree. 10D/15D materials should definitely be reserved for products used by people knowledgeable of and willing to deal with the tradeoffs – there are always tradeoffs for going lighter/stronger/cheaper.

As for the quality issues, this can be resolved by forcing a supplier to more thoroughly inspect their product. This typically will come with a price tag. As it stands, all but the most high-end products offered at RBTR are offered at low prices (imo) – prices for non-technical fabric at the local fabric store are, on the whole, higher than what we are paying for these technical fabrics. I am unsure what their quality clauses are with their supplier, whether their supplier needs to inspect a sample from every lot they produce, or whether they even test at all after the initial batch. I suspect somewhere in between, but I’d expect anyone listing a spec such as HH to be listing it at a very conservative rating, so that we don’t run into issues like this. With a listed spec of 2000mm HH, the Membrane Silpoly simulated aged test specimen should hit this spec no problem, but Stephen saw literally 25% of that. I won’t pretend to know what the minimum HH should be for a shelter; some here say minimum 2500mm, but there are big name tents on the market with 1500mm, and they sell just fine with good reviews. “That’s for each man to decide for himself” so the saying goes. But the quality control should be sorted by RBTR if we are testing their product in the same way their supplier tested it, and we are getting much lower results. We should at least be getting what we are paying for (the listed spec).

also, Dan, I think there is a little confusion. Most of the materials available from RBTR use a Sil/PU mixture to impregnate both sides of the fabric – to my knowledge, this coating is unsuitable for seam taping. Contrast that with the fabrics RBTR offer which have a Sil/PU coating on one side, with a PU (PE/PEU whatever the chemical composition is) on the other side, suitable for seam taping. Maybe you aren’t confused because you are actually designing, spec’ing, and actually producing good-performing shelters for the “mass-market”. But I and most other MYOG guys only have an outside perspective of the differences in what the mfrs are actually using to produce their fabrics or finished products.

Good point – I was talking about using different coatings on different sides and not blended coatings, as RSBTR does. I’m not aware of a rationale for doing that. Maybe it’s less slippery/easier to sew for the MYOGer (vs sil/sil) but it could be costs. A sil/PU blend wouldn’t have the costs/challenges associated with applying different coatings to each side. I’m hesitant to chalk it up as a “cheaper but inferior” fabric without a better understanding of what their rationale is, but I can see a fabric mill that struggles with weave quality issues (as shown) much preferring to use the same coating on both sides rather than trying to delicately balance two different coatings.

sil/pu blends are easier to meet EPA rules

importing avoids having to meet those standards

Interesting. You mean EPA rules for emissions (e.g. VOCs) during the production of the fabric? And thus irrelevant for imported fabrics? It seems like virtually all fabrics (including these) are imported, so the EPA rules would be much of an issue unless I’m missing something.

Mills use the blend due to the emissions of VOC’s being less of an issue. EPA rules have chased most of  the manufacture of silicone coated stuff overseas.  Maybe the overseas mills are also reducing pollution containment costs.

Had an inventor come by who was making hydraulic arms for a robot. He grabbed some scraps of silicone coated nylon which he bonded together in layers with tub caulk for his prototype. Talk about needing to withstand water pressure.

I do see the choice of tent fabric as being less a matter of trade-offs and more of a bottom line.  Sure, there are a lot of trade-offs in designing shelters and other gear; but the weather in this part of the NE USA this past week gave me some pause.  Wind velocities were reported above 50 mph in many populated areas, well below the peaks of higher mountains.

Add to this that I live in the focal point, about 600′ above sea level, of a mountain crescent that only partway surrounds my home.  When we get a wind storm like we did this week, you just know trees will be blowing down and the power will be going out.  The noise of the constant wind blast can be quite unnerving.  And towns opened shelters for folks who could not keep warm in their homes.

That is why fabric for a durable tent is not chosen with trade-offs in mind.  The bottom line is that the design, materials and precip resistance must be enough to provide confidence that a shelter will withstand severe weather, maybe not at the top of Mount Washington, but at average heights in the area.  And that is why for me an aged HH under 500mm in an unreinforced membrane 15D fabric does not cut it.  We want to pack light, but smart light.  The chief reason for using a tent is that it will provide adequate protection in storms.  Not that a dry place in which to eat, sleep and relax in rainy weather is not OK as well.

It doesn’t bother me any that you use this standard as your baseline for determining whether a fabric is good enough for you. I only question the use of the standard as an accurate representation of real world requirements. Even wind and constant rain which you describe is not accurately represented by the standard Suter test. The suter test places a burden on the fabric in a concentrated area well beyond what even the stormiest storm is going to apply to the sides of a shelter, IMO. This is similar to an argument I had about a test performed on a piece of EVA foam, using a large paper clip to apply a large pressure on a small area of the foam, then coming to the conclusion the foam was not good enough because the clip pressure caused the foam to fail. If a piece of foam passes this test, then fine, and you can spec that, but it is well past the real world expectations, and it is likely going to cost you more than a product spec’d according to a test that simulates real world situations.

Not many people driving around in bulletproof Hummers – you can buy them, and they will get you where you want to go, but they are usually overkill for what most people need in an automobile.

“That is why fabric for a durable tent is not chosen with trade-offs in mind.  The bottom line is that the design, materials and precip resistance must be enough to provide confidence that a shelter will withstand severe weather…”

I agree with your point that sometimes you need non-negotiable attributes like sufficient tear strength and waterproofness. Perhaps just semantics/different perspectives but I still think of this as a trade-off. The definition of a trade off is when you have 2 or more competing attributes (e.g. fabric durability and weight) that come at the expense of each other so you can’t optimize both simultaneously (e.g. the strongest fabric will never be the lightest). Thus if you’re in a position of needing a very strong tent you have to trade away potential weight savings, or vice versa (the builder of  a very light tent has to trade away strength). Anywhere along the spectrum from extreme light to extreme strong is compromising the other attribute and thus trading off something.

Anyways, I think your core point has to do with individual attributes (e.g. strength) which are non-negotiable and thus you’re not going to trade away any of that specific attribute. I guess it’s just different perspectives where you see this as not a trade-off, whereas I see that as a trade-off where the choice is clear (I’m not trading off any strength, therefore I’m trading off a lot of weight).

I’ve reached out to RBTR with regards to Stephen’s test report for the samples he had – I’m not sure it will get much attention, but we can see. They were interested in the reports of twisted threads in the Membrane silpoly samples provided, so maybe they will use it to investigate their supplier – not holding my breath, but just thought I would let everyone know that they have been directly contacted regarding the issue.

Michael B sent me three fabric samples.  One is another look at Membrane Silpoly which was the fabric tested above.

Here are the results.

Here are photomicrographs of each:

Membrane Silpoly Burnt Orange

1.1 Silpoly PU4000 Yellow

.77 oz Mtn Silnylon 6.6

These all show reasonable HH performance where aged performance exceeds the RBTR HH specification.  It is interesting to note that the Membrane Silpoly and the Mtn Silnylon both have twists in the fibers that produce voids.  However, unlike the original Membrane Silpoly sample, these are performing as specified.  It certainly appears that there is a manufacturing deficiency in the original sample that was tested.

The PU 4000 leaks occurred along ripstop.  The drop sizes at these leaks were tiny.