Looking for Silpoly

[Sam Farrington]

With the advent of improved polyester tent fabrics and coatings, a superlight silpoly tent should be within reach for MYOG.  But I’ve spent many grueling hours looking for the right silpoly for a tent, from all conceivable sources, including tent makers and fabric dealers in Europe and Asia, all to no avail; so thought an inquiry here might get me off the dime where I’m stuck.

Am looking for a material with a finished weight under one ounce, or very close to it.  It is available in a 15 Denier “membrane” fabric from RBTR; Dutchware, and others, but not with any kind of micro or macro ripstop grid.  Have found ripstop essential to prevent silpoly this light from tearing, or unraveling at small punctures, and a micro ripstop grid would be less detrimental to a waterproof coating than a larger grid.  The superlight nylons, like the 7 deniers from RBTR and Rockywoods have the micro grid, and all seem to agree it is better for this type of application.

I did find on RBTR a 15 denier polyester with a micro grid, but not a waterproof coating, only a DWR treatment.  Ordered some though for an inner tent ceiling.

Before you tell me to use DCF, please note that after reading everything available, including BPL forums, I’ve ruled it out for a variety of reasons, including the desire to avoid putting a lot of effort into a tent that would wear out much sooner than a woven fabric one.  There is a good discussion on the SlingFin site about this:
https://www.slingfin.com/blogs/the-beta/tent-fabric-101-nylon-vs-polyester-vs-dyneema-cuben?_pos=3&_sid=32380a9d7&_ss=r

Have also firmly decided that nylon is not the way to go for a tent canopy for all the well known reasons expressed in the above linked discussion and on these forums.  As a last resort, might use it for areas where the nylon is bowed out on the bias by a pole framework, as this would both limit the sagging, and support whatever sagging did occur.

It may be that 20 denier 1.18-1,25 oz/yd2 finished weight is the lightest one can go with silpoly, but am not giving up yet.  Know the fabric is out there, finding it with decent quality from someone who will sell ten or so yards of it is the challenge.

If you’ve read this far, thanks for listening.  Any and all suggestions would be much appreciated.

[Jerry Adams]

I’ve used my membrane silpoly from RSBTR mid for several years without ripping.

I’m sort of a fair weather camper, but I’ve been in 30MPH winds, maybe 40 MPH.  I don’t camp on mountain tops.

I reinforced the peak with a circle of the same silpoly to double the strength, then a smaller circle of 200D nylon.  The corners no reinforcement but it does go through flat felled seams so there are several layers of fabric.

There are several holes from fire embers, but they’re at the bottom at a place without much tension.

[Sam Farrington]

Thanks, Jerry.

Maybe I should order a swatch of what RBTR is selling these days for membrane.  Possibly, there have been some improvements.

My approach to selecting campsites is similar to yours.  Not trying to prove anything, and like to spend sleepful nights.   But high winds/precip can strike at night when the weather looked fine when pitching earlier.  Goes for both Colorado mountains and ‘hills,’ in NH; although in the Whites, it is possible to ascend 4000 feet from a trailhead in a day.  Maybe they are hills compared to the Rockies, but the winds can be just as brutal.

[Michael B]

As long as you don’t get angry at your tarp being blown away and decide to throw a stake in its general direction, you should be fine. The Membrane PU4000 seems easier to tear than the standard Membrane, but I agree with both you and Jerry; the standard membrane should be fine for most use cases, especially with some well-placed reinforcements, and I do think the fabric would be better with micro grid sort of ripstop. I have a pattern design for an X-Mid style canopy I want to make next, and have about 7yd of the Foliage color Membrane, but would like to make something out of that microgrid MTN silnylon someday. It feels solid for the weight.

one of my other rules I try to obey with the silpoly fabric is to align tension forces with my seams, as each of my felled seams has 3lines of stitches and 5 fabric layers to take the load. Obviously it wouldn’t work for every tieout or prevent such “tent peg incidents” from occurring, but the majority of issues should be covered.

[Jerry Adams]

yeah, same here, align tension forces with flat felled seams

I’m not convinced that grids are useful.  For one thing, if you have a bigger thread, then it tends to make bigger gaps so it’s harder to be waterproof.  I’ve never had rips that need to be stopped.

I’m not sure though

[Monte Masterson]

I’ve never heard of a 15d ripstop silpoly. I just made a small trapezoid tarp out of the Dutchware Xenon 1.1 ripstop polyester. Dutch claims it has a finished weight of 1.1 oz, but that’s not true. Weighs about 1.25 oz on my scale and it’s pretty accurate. Dutch is pretty high on his Xenon Wide though in terms of HH and quality. He says it has a finished weight of 1.2 oz. Might be a good choice.

To me the Slingfin article makes more of a case for nylon than silpoly or DCF. I suppose it’s how you interpret the writing. And I see they make all of their shelters out of nylon. Again I have to wonder why virtually none of the mainstream tent manufacturers use silpoly, at least nothing lighter than 20d. My next project will be made using the 7d nylon 6.6. I’ll keep my eye out for a sub 1 oz ripstop silpoly though.

[SIMULACRA]

There was quite a lengthy thread here maybe around 2015-2016 talking about this very thing. Silpoly membrane and ripstop. Just searched couldn’t find it. Was very informative at all angles. Will keep digging

[Rex Sanders]

Tent designer Mike Cecot-Scherer has a different perspective:

https://backpackinglight.com/standards-watch-mike-cecot-scherer/

“If [tents] are properly reinforced, [they] will have no tear strength issues. Misguided attention to tear strength is one of my pet peeves.”

He emphasized that point in a more graphic fashion for interview part 2, focused on tent design. Should appear here … someday.

— Rex

[Rex Sanders]

You might find this long, detailed 2016 thread relevant:

https://backpackinglight.com/forums/topic/silpoly-tarp-durability/

Maybe what @simulacra was looking for?

— Rex

[SIMULACRA]

haHa! nope, not that one Rex :) I did find that one in my search but it’s not it. It was quite deep and informative

[J-L]

Sam, I don’t think the fabric you are looking for exists yet. I also think a gridstop helps with tear strength.

Rex, I’ll be interested to read Part 2 of your interview. I have seen that quote of Mike’s about the focus on tear strength elsewhere, however, I have also wondered if isn’t a bit mis-guided now. When Mike was in the industry many years ago, tents used higher denier nylon fabrics that probably were excessively strong. Now with companies using 7D and 10D fabrics, tear strength would seem to be more important. Maybe at 7D or 10D, you need the extra strength of nylon vs polyester?

@simulacra Is this the thread you were thinking of?

https://backpackinglight.com/forums/topic/strength-of-93-oz-membrane-silpoly-vs-1-24-oz-silnylon/

There are several good quotes in there, including:

I highlight tent because after speaking with kyle at RSBTR, he clearly stated that the .93 Membrane is only recommended for tarps. He said that the force is much more even on a tarp whereas the design and shape of a tent or mid will create odd stress points and could cause failure

[Roger Caffin]

I also think a gridstop helps with tear strength.
It can do so with uncoated fabrics.
It may do so with the old PU-coated fabrics (which had poor tear strength because of the PU coating).

However, my tests indicated that ‘ripstop’ adds nothing to the strength of a silicone-coated nylon fabric, but it does reduce the HH rating badly.

As for the stress-distribution in a tarp or a tent: that would depend hugely on the design of the shelter, the way it was sewn together, the way key points were reinforced, how the shelter was pitched …
Don’t even try to generalise.

Cheers

[Rex Sanders]

@johnnyh88 FYI: Mike never left the industry, still designing tents for big companies and his own, including very light fabrics.

“the design and shape of a tent or mid will create odd stress points and could cause failure”

Maybe that’s why some professional tent designers get it right, and others not so much? Designing to extreme weight or cost targets triggers serious compromises.

Many voices, many perspectives, like the very old story of blind people describing an elephant. Hope we can learn something from all of them.

— Rex

[J-L]

Thanks, Rex. I thought Mike left to design his own tents.

My point about that quote is that even the founder of RBTR had doubts about Memrane Silpoly in some applications. And then Jerry just goes and makes a mid out of it :) It seems to work, but he is braver than me.

Roger, I know you have done those tests. But I don’t think the results are fully applicable to lower denier silpoly or the micro grid that Rockywood’s 7D silnylon has. They have different coatings, materials, and maybe even different weaves.

[Roger Caffin]

I don’t think the results are fully applicable to lower denier silpoly or the micro grid that Rockywood’s 7D silnylon has.
I believe they still apply as it is the mechanisms underneath the raw results which I look at.

This is a light silnylon put thru an ASTM tongue test. Note carefully what has happened. The ripstop threads have done just about nothing: the load was spread right across many threads in the fabric by the silicone coating. This is why a silicone coating adds so much to the tear strength of silnylon.

Contrast this with what happens with the old PU coating. It was far more ‘rigid’, and focused all the force onto a small area over a couple of threads. As a result, the tear strength was seriously reduced over the raw fabic.

We have known about both of these factors for well over a decade (eh, maybe several decades?). But the Marketing guys still think that adding the word ‘ripstop’ adds glamour.

Cheers

[Sam Farrington]

John, re: “I don’t think the fabric you are looking for exists yet.”

If you are right, then I should take a look at what is the weight penalty for using 1.24 oz/yd2 silpoly vs  1.06 oz/yd2 sil or sil/PU nylon.  To do that, I’ll assume an outer fabric covering two vestibules, one on each side of a side-entry design, and a fly covering the sleeping area between the vestibules, with some overlap to prevent leakage.  Have done that, and get roughly 7 sq yards for a comfortably large solo tent.  That could be more or less, depending on the design and size you have in mind.

So I get 1.26 oz.  That is not too bad a penalty for losing the worst issues with nylon, including silnylon:  sagging and wrinkling due to expansion caused by precipitation, humidity and/or temperature drops; absorption of water making it difficult to pack up and carry a wet tent; greater difficulty getting into and out of the tent without getting wet; and moreover, the sagging and wrinkling that weakens the structure of a tent, because the fabric often becomes no longer able to work in mutual conjunction with the poles to increase the tent’s strength and resistance to strong winds and precipitation.

Then there is the question of whether losing the nylon for a slight weight penalty creates other types of penalties; such as loss of  packability, bias stretch, or abrasion, puncture and tear resistance.  The RBTR 20D silpoly has as much if not more of a soft hand as a 30D silnylon.  Neither material stretches much on the grain, except nylon when it expands undesirably as noted above.

And using models, I’ve found that the bias stretch of woven polyester is considerable. Abrasion, tear and puncture resistance are not quite as good as nylon, according to RBTR, but after looking at BPL and other forums, such as Reddit, I could not find any complaints about the 20D, although with respect to punctures, abrasion and tearing, there were a number of complaints about “membrane silpoly.”   Note that I’m not a trained lab technician, so have only experiences of others to go by.

Normally for me it is: more weight=bad, and less weight=good.  Failure to follow that most often leads to over-design and it’s back to focusing on KISS.  And all the little weight penalties add up; so the de minimus principle does not apply to just one penalty.  It is not about the small weight difference; but rather how the better nylons and polyesters will function in the field.

Roger, re:  “However, my tests indicated that ‘ripstop’ adds nothing to the strength of a silicone-coated nylon fabric, but it does reduce the HH rating badly.”

But what if the fabric is polyester, and it is a micro grid, and not a conventional ripstop?  Brother Nisley has said:  “In addition to having a very-high quality sil/PU coating, this fabric has periodic increased thread density, rather than larger threads, to create a riptstop effect.  I don’t recall having seen this before; it is a very effective way to increase the tear resistance without reducing the HH do [sic] to having bigger threads the coating knife has to jump over.”  – from 12/7/15 post on forum topic 108230, titled “0.7 osy coated nylon,” and referring to the Rockywoods 7D.  Holding a medium gray swatch of it up to the light, the micro-grid is as clear as a bell, and of similar dimensions as other micro grids.

Everyone:  Reading through all the prior threads linked above, I noticed many statements that were incorrect just because the threads were old, including statements from me as well.

One constant that comes through the confusion is that we need to be open to new ideas.  So as suggested above to John, I’ll eat the 1.26 ounces.

Thanks for your many helpful comments.

[Roger Caffin]

But what if the fabric is polyester, and it is a micro grid, and not a conventional ripstop?
Why should that solve the world’s problems?

The bigger ripstop threads will make larger gaps between the threads, leading to leaks at the threads and a lower HH. Polyester, nylon, whatever – this is a function of the mechanical size of the threads.

A micro-grid is probably better than a conventional large ripstop pattern. But having got that far, why stop? Why not recognise the lack of functional benefits from any ripstop construction?

The industry creeps on slowly towards a future without ripstop construction, but there is always resistance from marketeers and ignorant retailers. Mind you, we have the same battle over fire-retardent treatments, only in this case there is a severe health effect from the chemicals (and back-pressure from the chemicals companies), and State Health Depts are taking notice.

Cheers

[SIMULACRA]

John,

I believe so, will have to read through it. What I remember gathering from what I read years ago, was, in a nutshell, that ripstop didn’t give a significant difference in tear strength. But I’m no expert there

[Tuukka U]

How about the Xenon .9 from Dutch? Not ripstop, but I remember reading about someone comparing it to RSBTR’s Membrane 0.93 and the Xenon came out significantly stronger, although tested by hand

[Michael B]

Is there a difference between tear strength and tear propagation, and if so, are they both standardized with test criteria?

[Roger Caffin]

Yes, a big difference.

Tear propagation is covered by ASTM and DIN and ISO standards, and is meant for measuring the strength of thin, usually plastic, films. It is not all that well-known.

Tear Strength is covered by Standards, is well known and there are a number of commercial instruments for measuring it in various ways. Indeed, there are a number of slightly different uses of the term, as reflected in the different test methods used. This is the one we would normally consider. That said, it is fairly intuitive.

Cheers

[Monte Masterson]

“but I remember reading about someone comparing it to RSBTR’s membrane .93 and the Xenon came out significantly stronger”

RSBTR describes their membrane .93 as having a “Sil/PU” coating whereas Dutch says his Xenon .9 is “siliconized.” I take that to mean the Xenon .9 is straight silicone and not a PU mix like RSBTR’s membrane. Wonder if that makes the Xenon stronger?

[Michael B]

Without each of the companies stating explicitly what their coating is, we probably have no way of knowing if there is even a difference. Best to privately test each of the materials if their standardized specifications are not provided.

[Roger Caffin]

It is more complicated than that!

A Chemicals Co (eg Whacker) sells the latest coating mix to a coating plant on Asia, who then applies it and sells the fabric around the world. It may well be that many coating plants don’t even bother to test the results, relying rather on the Chemical Co.

Cheers

[Sam Farrington]

Roger, re: “Why not recognise the lack of functional benefits from any ripstop construction?”

And: “A micro-grid is probably better than a conventional large ripstop pattern. But having got that far, why stop? Why not recognise the lack of functional benefits from any ripstop construction?”

I guess the answer is that no evidence appears of the lack of functional benefits of the micro grid.  Since it is found in some of the lightest fabrics (Rockywoods 7D, RBTR 7D & 15D Camo, and StoS 15D tarps), I’d give the vendors the benefit of the doubt about whether they know what they are doing until it is shown otherwise.  It is certainly logical that the micro grid would help to strengthen materials like membrane silpoly that have reports of failure, like this one on Reddit in 2016:  “I have a membrane silpoly tarp.  It is very light and waterproof, but very fragile (I tore mine on the first night out).”

Re: ” It may well be that many coating plants don’t even bother to test the results, relying rather on the Chemical Co.”

And it may well be that the vendors know even less.  But this is speculation.  Whether it is so, depends for me on my experiences with the vendor company.  If they are accurate about some things I can verify, like weight and HH, I’d tend to trust them more about things I cannot verify, like value of a micro grid or tearing in extreme winds.  If they are not accurate, it would be to the contrary.

This underscores the suggestion I’ve made many times on BPL forums; namely that we order a meter or yard (not a tiny ‘sample’) of material, check the weight, and for a supposedly waterproof material, obtain or find  on BPL a test of HH, including after simulated aging.  Then recheck the results against the vendor’s claims.  After a while, it becomes obvious who is spouting BS, and who is at least making an effort to obtain and market better products.  IMO, RBTR is, but some who will remain nameless are not.  For those of us who spend months, and sometimes years making our own gear, I think this is what we have to do to benefit from MYOG.

P.S.  There is a lot of talk on BPL about tear resistance of woven tent and tarp materials as if it were the sine qua non.  I remember the demos of vendors struggling to tear Cuben fiber, the same material that Richard Nisley tested and found leaked like a sieve and that I could cut much more easily than silnylon with a sharp utility knife.  Also remember your comments about almost never experiencing  tearing in your tents.  My experience is similar, with no tearing in tent canopies; only some leaking at stress points and abrasion of floor bottoms, both after many years of use.  So I think that abrasion and punctures should be of at least equal concern, some exceptions being when there are multiple reports of rips developing, or the fabric unravels when cut.

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