Looking for Silpoly

HH tests (or whatever) have limitations too.  Different lots of fabric are different.  It changes with age.  It’s hard to correlate HH results to actual usage…

I don’t have a problem with a bunch of sometimes conflicting data.  There will never be an absolute yes/no answer about ripstop or anything.  But I’ve never had fabric rip so I’m not too worried.  And I’ve never had a significant water leaking problem.

I like experiences from people that made a tent with some fabric that worked, or failed.

I wonder what that tarp failure on the first night of usage was?  Was that something that would apply to me?  Was it constructed properly?  Was it in a hurricane?…

I took some of that lightweight silpoly and started a rip, and I could easily propagate it pulling it apart, but I won’t do that on my tent.   Hard to correlate that to anything that applies to me.

I should sew on some tent stake loops, apply weight, see what happens.  That would be representative of actual use.

I had a tent fail once, at the peak.  But it was very windy and it was an experimental design with a large opening that caught the wind.

I’ve had misting, but your skin can feel a tiny amount of mist.  Not enough to get gear wet.  I always assume some water can get onto gear even inside a tent so I put it into a waterproof bag.  “belt and suspenders”.  Condensation on the inside sometimes happens which can get knocked off onto me and my gear.

Lots of discussion about one fabric being “better” on one parameter or another. I’ve even participated in some.

But what’s more important are other things I’m learning from designer interviews and personal experience as a user:

– Specs aren’t everything.
– Many standards and tests aren’t reliable. Or even repeatable.
– A “good enough” fabric is … good enough. But that depends on MANY other factors.
– Choosing the “best” fabric or shelter based on one or two parameters usually leads to serious compromises elsewhere.
– A few patches of high-quality gear repair tape can quickly fix a lot of problems, much lighter and cheaper than different fabric choices or shelter designs.
– Good design can overcome many “inferior” fabric specs.
– But good designs are rare – especially from well-known companies working under distorted incentives. “OMG, your tent is 4 ounces heavier than this other one!”
– Good design by necessity ALWAYS makes a series of tradeoffs. Those tradeoffs might not work for you. An extreme example: the perfect PCT peak-season thru-hike shelter wouldn’t last long on a Denali winter circumambulation. But carrying a 10-pound bomb-proof tent on the PCT doesn’t make sense either.
– Your ”perfect” shelter design, fabric, and other components might still suck because you got stuff made on a bad day. Nobody in the supply chain does 100% QA/QC for every parameter at every step.
– But some sources are definitely more reliable than others.
– Good product use skills still count for a lot.

If good product design was easy, we’d have to argue over something else in these forums :-)

Carry on.

— Rex

I have a hunch that Sutter testing exaggerates the negative effect of ripstop on water resistance.

How?

Mechanical explanation for the above please.

Cheers

I don’t think sutter testing correlates to dynamic, stochastic (rain) pressure very well. Under a static wall of water, of course leakage will occur first, and rather early, at the abnormally large interstices at ripstop junctions. Under dynamic rain pressures, I’m  not sure those abnormally large interstices are as significant. Easy experiment for a retiree.

Easy experiment for a retiree.
NOT!

I have done some literature searches on this a few years ago, and afaik, nothing has been done in this area for fabric at all.

I did find a modelling paper on the impact pressure due to raindrops hitting a steel plate -a colossal and very fast pressure spike in the middle of the drop, but the results are not relevant to fabric as it behaves a ‘little differently’ from an inflexible incompressible steel plate.

Some other papers I have found cover the impact of raindrops on soil and sand. It takes a certain amount of energy to move a grain of sand, so erosion tends to be a non-linear thing, and this is of interest to Gov’t Ag Dept’s etc. Not really relevant to fabric though.

Part of the problem is the sheer microscopic scale of the interaction: you are looking at the the area between a couple of crossed threads, and a single drop of water. Commercial pressure sensors on this scale are not readily available.

Another part of the problem is that most pressure sensors are designed for static measurements (like one reading every minute), but the time scale for a raindrop hitting a surface is milliseconds or even microseconds. The dynamic range of pressure can be colossal.

My field studies suggest that, at least for a smooth surface such as a coated fabric under high RH conditions, the inner surface of a fly can be host to a very thin film of condensation. Normally you might not even notice this. But with the fast pressure spikes from each raindrop on the outer side of the fabric (as mentioned above), tiny drops of water can be shaken off. This seems to be the source of the apparent spray of water some people report: not leakage through the fabric but surface water shaken off. Well, I have seen this in the field myself.

Cheers

quick and dirty experiment – 0.93 oz RSBTR silpoly

weakest, just to test limits.  tent stake loops just through the body of fabric with no reinforcement.  1 mm zigzag with 2 mm straight lock.  10 pounds load okay.  Under about 20 pounds it ripped:

Try it with flat felled seam.  1/2 inch seam allowance so the flat felled seam is about 1/4 inch.  It held up the 26 pound lead sync lab brick without failure:

I just tied it and hung it vertically.  This is what the ridges of my mid are.  This is the most critical.  I’m pretty sure 26 pounds is more than anything I’d experience, the stake would pull out before that.

I think this silpoly is strong enough for normal use.  Maybe mountaineering would require something stronger.

close-up.  Just playing with phone close-up

Hi Jerry

I’m pretty sure 26 pounds is more than anything I’d experience, the stake would pull out before that.

Yes, and no. That is a good test for a static loading, and my compliments on doing it. But what about a dynamic load: the fabric flapping in a storm? I am NOT criticising; just stirring you on to more testing! More real data!

Mind you, a dynamic load is going to rip a tent stake out faster than a static load. But the point of the comment – YES. I have seen concerns about whether a 200 lb string is strong enough to be a guy rope – ha.

Cheers

good point

I was very careful to keep it a static load so the brick didn’t drop and put a hole in the floor

Thank you all for this interesting discussion and information and direct experimentation!

I found this past discussion https://backpackinglight.com/forums/topic/89134/ about the value of adding some shock absorption to guy lines.  Would this help for these very light sil poly fabrics?

Shock absorption:
Yes and no.
Using my tunnel tent as an example: ANY stretch in the ground-level guy ropes at the windward end could destroy the tent. (I have videos!) I use short 3 mm loops of cord there.
But, at the lee end, I use 150 mm long loops of strong 4 mm bungee cord (so 2 cords in effect) in order to put lots of tensin into the fly fabric.

To generalise then: if you let the fabric flap around (especially at the windward side), expect a lot of trouble. But using bungee at the lee end to maintain tension can be good.

Such fabric tension is extremely unlikely to do any damage to the fabric by itself. Poor pitching, poor design, poor manufacture: they will cause damage.

Cheers

I suspect there’s another issue beyond HH and strength, and that is bias stretch.

These very light fabrics are surely going to stretch significantly more under wind-load.

That means the panels will scoop more and catch more wind.

And that means more flapping and strain on the anchors.

Probably not an issue for camping in the woods.

Not so sure about above the treeline, though.  For exposed camping, beginning to verge on stupid-light??

definitely.  And ridges in mids are on the bias – a design defect to work around, the tent flaps in the wind

and the solution is to take stiff webbing and sew it on the ridge from the peak to the corner.  I used the same silpoly fabric.  3 inches wide on the grain.  Fold three times to make a 1/2 inch strip of 6 layers.  Sew along strip on each edge to keep it in folded.  Then sew to the ridge, one row of stitches down the middle

I did one ridge reinforced like this, the other ridge like normal.  On a windy trip, the reinforced ridge flapped much less.  I didn’t test to failure though, this could be more aesthetic.

I reinforced all ridges and have used that for a while

Bias stretch
I agree most definitely.

It is easy enough to handle this in my tunnel designs: you can see how the forces will be oriented and how to reinforce. Some other designs leave me wondering though: the orientation of the forces is not at all clear to me. In some cases I suspect there could be significant shifts in the forces depending on the wind.

Can one use reinforcing (seams or tape) to help handle this? I suspect so. But such reinforcing would need to be supported. If you run a seam down the middle of a major panel in a pyramid (for instance), you would really have to add a good ground-level anchor and use it.

Cheers

Does the very act of creating the felled seams on the ridgelines mitigate the bias stretch at these locations? I mean, you would think 3 lines of stitches in line with the load would keep stretch to a minimum- at least it felt that way on my tent – maybe I am misunderstanding what is being talked about here.

Jerry, regarding mids and ridges being on the bias, is this always the case? I’m not sure, owning nothing from either, but I have a hunch that Locus Gear does their ridges selvedge-selvedge, but that MLD sews theirs bias to bias.

I like your solution of reinforcing the ridges, and – off topic – I think this should definitely be done with DCF, where bias instability invites plastic deformation. Come to think of it, is silpoly susceptible to permanent elongation? Nylon’s elasticity seems to protect it – although I’ve a silnylon mid that has four deformed ridges above the tieouts- but how about polyester subject to sustained high loads and then wind pulses?

does flat felled seam with 5 layers of fabric on ridge mitigate bias stretch?

No.  That’s what I’ve observed.

you could have the ridge on the grain and mid panel on the bias.  I tried that a little.  But it causes another problem.  Then there’s a direction from the middle of the ridge, along the grain, to the stakeout on the center at the bottom.  That pulls down the middle of the ridge, so the ridge is no longer a nice curve.  It reduces headroom inside.  I have a picture somewhere.

when I put ridge on the bias and reinforced it, that worked pretty good so I stopped experimenting

What’s conventional is to have the sides made of two panels.  There’s a flat felled seam that goes from the peak, to the center of the bottom.

I’ve seen the fabric laid out sideways.  Since the fabric isn’t wide enough (60 inches) you have to have a flat felled seam sideways to sew two pieces together to make it go from peak to bottom.  So, there’s a flat felled seam sideways, rather than going from peak to bottom.  You still have the ridges on the bias so it doesn’t change that.  Maybe this is better?  Maybe arbitrary?  If you have that sideways seam at the top, rather than the bottom, the total length of seam is less, maybe that’s good.

I’m sewing up a 4-sided rectangular pyramid tarp now using RBTR’s 20D silpoly and bias stretch is my biggest concern. The 20D silpoly fabric stretches much more on the bias than other 30D silnylons I have used. I don’t think the fabric or my tie-outs will fail. But I am worried about how the final shape will actually turn out and how flappy it will be in the wind. The high bias could also create large, undesired gaps along the ground in between the corners.

I sewed up a 6-sided pyramid tarp several years ago using Dutchware’s Argon silnylon – it’s no longer sold, but I think it was a 15D silnylon. Bias stretch was less of an issue on that tent due to the 6-sided design as the main seams weren’t on a huge diagonal like on your typical rectangular pyramid tarp.

Jerry – your solution seems like it would work very well. I might implement it on my tarp. Thanks!

looking at pictures of MLD and Locus Gear, also oware

I think they all have ridge on bias and a seam going from the peak, down to the center bottom.  A little hard to tell from the pictures

I could swear I remember someone with the seam going sideways

Pyramid tents are sort of a commodity.  It seems like it would be difficult to have a premium price.  Competition between them.

Lots of weird shapes for tents that may or may not be better.  Then they can claim a particular unique design is better and charge a premium price.

Maybe some of those weird shapes actually are better, or better for a particular person or usage.  No judgement by me.

I’ve had/have rectangular mids from Black Diamond, MLD, and Oware. All had ridges sewn on the bias. Black Diamond and MLD used flat-felled seams (or variations). Oware seems to use a rolled seam for their ridges. All are plenty strong.

Re:  “I’m sewing up a 4-sided rectangular pyramid tarp now using RBTR’s 20D silpoly and bias stretch is my biggest concern. The 20D silpoly fabric stretches much more on the bias than other 30D silnylons I have used.”

Haven’t worked with pyramids, but would like to add a few points:

When I got started on BPL to try to learn to make better tents, Roger provided me with a lot of help, some of which involved a good number of HH tests.  I soon became aware of his many photos like the one above showing drops leaking along the lines of ripstop grids at the points of failure of waterproof fabrics.  This was at a time when it was almost impossible to obtain light and durable silnylon that in the long term would resist leakage in prolonged and heavy storms.

Around that time,  there was a thread seeking to debunk HH tests as a useful tool for MYOG.  After reading the arguments, and based on Roger’s many tests, I was convinced that the HH tests are very useful, and this was later confirmed for me by the sometimes maligned tests done by Richard Nisley, who stepped in and HH tested many fabrics, including some I submitted under his simple protocol.

Since then, much time has passed, and Stephen Seeber has stepped in to provide HH tests  reported on the gear forums.  We have corresponded at some length, from which I’ve learned how difficult it is to repeat identical results, because as was pointed out above, there are so many variables involved in HH testing.   Steve has even paid private labs out of his own pocket to verify a number of issues that have come up in this regard.  And he has promised on these forums to come back to us with his conclusions,

What seems clear to me from Roger’s many photos of failure on ripstop grids is that this is a weak point, and a problem when it occurs at lower water pressures.  It is why I quoted Richard’s comment earlier about micro grids, or mini ripstop as it is sometimes called.

Since many have alleged that polyester is a weaker fabric than nylon, I was concerned about RBTR’s use of a regular ripstop grid on its 20D silpoly, which is claimed to have a blend of sil and PU on both sides of the fabric.  That is why I asked Steve to HH test the RBTR silpoly, as he did and reported on these gear forums.  Since then, Steve has reported an HH of  over 4000mm after simulated aging using the aging protocols used by Richard and others.  For more we will have to wait for Steve’s further report.

So with everyone’s assistance I’ve decided to use the RBTR 20D silpoly.  It is a woven material, so has more stretch on the bias than on the grain, although I’ve not observed more bias stretch than observed with a silnylon with the same denier (20) and similar weight (1.24 oz/yd2).  So am puzzled by John’s results.  Note that unlike nylon sagging, the bias stretch is elastic, and retains its original shape when not stretched.  Would have liked to use a microgrid ripstop, but am in the process of redesigning a tent to offset the additional weight of the 20D silpoly, and will eventually report on the outcome.  Will report sooner if run into any stretch issues that allow enough wrinkling to allow flapping.

Just to clarify my comments upthread about HH testing and ripstop. I pay attention to every post with HH data posted by Richard Nisley, Stephen Seeber and others. It’s the best information we have about fabrics’ water resistance. But I’ve observed a correlation considerably less than 1 when comparing fabrics with similar HH under shower pressure. Some fabrics do considerably better than their HH and others a bit worse. I have no idea why. But I think we would be better served by a dynamic test that simulated raindrop impacts on a tensioned piece of fabric – basically a simulation of field conditions with severe and hyper-severe rain. I do think that HH tests of pre- and post-aged fabrics are super valuable for predicting coating durability, and don’t think that a dynamic test would offer much extra for that type of evaluation.

With respect to ripstop, consider a plain weave silicone-coated fabric that tests at 2000 mm HH, and a ripstop silicone-coated fabric that also tests 2000 mm HH. I think the latter is actually more water-resistant, and will behave so in the field, for its leakage under 2000mm of water column pressure will only be at the ripstop junctions, as Roger’s picture upthread shows, while the plain weave will be springing random leaks all over the place. That’s just a hunch, and I could be totally wrong.

An interesting theory which I can neither confirm nor deny …
Some thoughts off the top of my head:
The ripstop fabric may have a heavier coating to get the same HH, and therefore be a bit heavier overall
The ripstop fabric may degrade in use a little faster

These are just THOUGHTS.

Cheers

Re: “But I think we would be better served by a dynamic test that simulated raindrop impacts on a tensioned piece of fabric …”

Stumphges,
That is logical, but some years ago, when Black Diamond stopped using Epic Malibu for its single wall WPB tent, the fabric became available from a number of vendors.  I took a garden hose, and adjusted the nozzle for the narrowest most powerful spray, and put the nozzle right up against the fabric (forget how the fabric was suspended).   Tightly enough so that no water was leaking out around the nozzle.   No leakage occurred through the fabric; or in other words, the water flow was completely stopped.  Granted, my water pressure (2 gals. per minute) may be not as high as in some homes served by public water supplies.

Also sent Roger some samples of the fabric, and he tested it to around 1500mm HH, just barely to the waterproof standard .  It held up to close to that HH; but then an effusion of water came through the fabric.  Not surprising, given the many complaints that led Black Diamond to change to another WPB fabric.  Those episodes persuaded me that fairly high water pressure is needed to show how well a tent fabric will withstand wind blown rain.  I think that is due to the pressure needed to test a fabric for just a few minutes vs. the effect of, say, and all night heavy downpour of wind blown rain that might wear down the coating.

Sure, you can set up a fabric to be exposed for many hours to the same degree of a rainstorm; but I don’t think showers will do it.  There are some videos on You-Tube that have been reported on BPL, of fabrics being shower tested; but not much info was provided on the ones I looked at.  It was clear to me, however, that a tent with walls at or near horizontal in places, and/or that puddles water under strong shower tests, is the most likely to fail.

But who is willing to run a shower set up for many hours or even days.  I’m not, because it would deplete my drilled well, and we have had a number of long dry spells lately that have caused some of my neighbors’ dug wells to fail.  Water could become the next gold when we get further into global warming.   Just think, Fort Knox full of water.

So while there are a lot of variables with HH testing;  but combined with protocols on simulated aging, I think it is the best way that we have to evaluate waterproofing of tent fabrics that will be exposed to heavy rainfall over extended periods.  I’ve also experienced occasional hurricanes in the area that drove water through my walls and windows, while  that never has occured during normal rainfall.