Cuben – The 422 mm hydrostatic head dirty little secret

"I can't help feeling you have misinterpreted what Richard was driving at. My understanding is that he was shocked by the discovery that Cuban Fiber fabric had such a low pressure rating, when we were all expecting it to be like heavy builder's plastic. Who made the tarp he tested, and whether it has a floor or not, are largely irrelevant to his discovery"

My point was a weak one based on thin anecdotal evidence, but all I was trying to say is that my real world experiences with cuben indicate a HH much higher than 422mm.

So hopefully through the more scientific testing we can reach a reliable conclusion on 0.7oz cuben and other variants. I'm most interested in knowing the HH of 0.7oz cuben, and whether the heavier variants (1.26oz and 1.51oz) fare better.

about cuben is that it doesn't sag like silnylon, a taut pitch matters. As for all the hand wringing about knee pressure etc. THATS why ground sheets are used ,cuben would make a good one.

This has been a very interesting discussion – although some of the edges of it have gotten a little overly warm at times. But I think I'd like to reiterate, restate, and clarify a point that has been raised but not as clearly as it perhaps should be. That is the idea that in any single wall shelter in significant rainfall, you are almost always going to find some moisture on the inside of the fabric. I've certainly experienced this under a variety of tarps and tent flys and whatnot, made from various materials-4-mil poly, PU coated nylons, silnylon, etc – over 40 years of backpacking. Now, we have seen here some very enlightening scientific discussions of water vapor and liquid water behavior with regards to transmission/evaporation/condensation, and I find that interesting. But in the end, if we are almost always going to find some moisture on the inside of a single wall shelter – regardless of how much HH it can handle – then it may not be all that significant whether it is from condensation, "misting" or leakage, AS LONG AS IT STAYS A VERY SMALL AMOUNT.
Yes, I think it is valuable information to know what the HH of the various fabrics are, both as new and after moderate and extended use. I'm looking forward to Richard and Roger testing many more samples of Cuben at different weights. If I ever have enough cash to afford a cuben shelter, it might be useful info :).
AND I think it is even more useful to know that if you want to travel really light (which is the main reason for using a single walled shelter) you have to deal with the idea that you will probably have some moisture on the inside of your single walled shelter – so plan for and deal with it.
And IF you want to stay REALLY dry in big rain, you want a double-walled tent in some form or other – which might include using two tarps.
In other words, lots of useful information here and I thank all those who have added to the discussion.

I'm a little tired of the insinuations that I am not a scientific type.
Here is the OP again;

"I hydrostatic head tested a new MLD Grace Duo tarp today. It was previously set up in my yard during moderate winds and rains for only 3 days total use. Afterwards the hydrostatic head tested worse than most silnylons at 422 mm H2O. I tested 3 random areas and got the same results in each spot.

I AM SHOCKED! I also measured the air porosity and it is 0. This means it would serve well as a sail but it is a poor solution for heavy rain protection. Has anyone else ever tested the hydrostatic head of Cuben"

Now, the first thing I would have done after being shocked would have been to actually test the tarp to see if the HH reading I got had any relevanceto actual performance. I would do this especially before declaring that this weight of Cuben is worthless for rain protection. If I was shocked I would question my belief that HH is so important and think maybe MLD knows something I don't know. I don't see any science here and for me this particular person loses credibility to certify anything. What, now we don't have to test any gear in the real world, we just attach it to a machine? Go ahead Roger, take that statement to show I'm not a scientific type.

The Op set the tarp up in his yard for 3 days of rain and did not check once to see if rain was coming through? The OP reads as if the tarp degenerated after 3 days to a 422 rating. This is all very poor science. The OP claims to not have tested the HH of the tarp before the 3 day rain. This is laughable.

Brian Austin, I'm curious about your experiences with Mylar and it's quick degeneration. Can you fill us in on your experience with it? Do you know anything about Cubens Proprietory version of mylar? The 4 oz Cuben I split apart yesterday is holding water just fine. Just one half of it, after the trauma of separation, is holding water and won't leak even after applying pressure and scraping with ice cream type spatchulas. This test so far has been with the dyneema side facing up, where the dyneema strands are protecting the 'Mylar type' layer. Not only is there a Mylar type layer there to repel water but we do have to consider what the probable substantial effect of the adhesive is that holds these elements together.

Also, has BPL or anyone else concluded what misting is or is the jury still out?

Dan – As I think I'm the only Paul that has taken part in the discussion, but I didn't say anything about Mylar or its degeneration, I think you must be referring to someone else.

Sorry Paul. I changed that to Brian Austin now. :>)

I have seen quite a few posts on various forums using the term leakage. We should make it clear that the only place anything has leaked so far is on the machine.

This is a very interesting thread. I'm eagerly awaiting the results of further testing but I tend to agree with Dan in that there is more to the equation than HH testing.

I'm curious to know if any of you are familiar with this shelter and what your opinion might be http://www.lightheartgear.com/LightHeart_Gear/Cuben.html.

Roger, here is a quote of yours from the first page; "Looks as though the way the Mylar bonds to the Spectra threads actually weakens the Mylar enough that water can get through, especially after a few packings. That is not unexpected – in hindsight."

I'm curious what you mean 'the way the mylar bonds to the spectra'. I'm serious here and in no way mean to take you apart like I did that piece of Cuben Fiber I'm testing. What I'm driving at here is that perhaps there is something about Cuben that might cause it to not do well in a HH test but that it might excell in the field. If you have mylar sitting on top of strands of anything and you compress that mylar further down around those strands, a situation could develope where the mylar is stretched to failure. This could be something unique to Cuben. Polyurethane coatings no doubt stretch more. The point is that we could have a fabric that just does not do well in a mechanical test but performs great in the field. This would only apply to the very lightest Cubens that are in a league of their own anyway. I have been working with the lighest mylars and relative to urethane and urethane/silicone coatings there is not as much give I don't think. I recently tested a urethane patch on a slit I deliberatley put in a piece of Cuben and the patch itself was very flexible and could spread 1/4" without failure. I don't think an extremely light sheet of mylar can do that!

Hi Dan,

I am really glad to see you jump into this with both feet.

This has been very interesting reading. I have used a lot of Cuben Fiber over the years (about 8) in 5 different weight products. Most has been the lightest, around .32 but I have on hand and use some in .47, .66, .96 and some as heavy as 6 ounces per squard yard.

When I made my Cuben Poncho / Tarp back in July of 2005 I hung it out in my back yard most anytime we had a good rain storm. I spent a few hours in my Cuben Hammock under the Cuben Tarp during a thunder storm with rain coming down so hard one afternoon I didn’t want to move. I did get some misting but mist and condensation is something you just learn to live with or stay indoors.

Feeling it might be about time for someone here to “Eat Crow” I did a search for a few good recipes.

Crow Busters Recipes

Hey, it says crows are a non-songbird species. They talk though. I don't eat creatures that talk. Haha

Seems like we have to get to the bottom of Misting. I can understanding a raindrop blasting through a silnylon that ended up in the seconds lot after not passing the parachute test but not Cuben. I'm pretty sure there are at least 2 types of misting. One is the raindrop forcing and dispersing water through a poorly coated fabric and the other is caused by vibration from heavy rain knocking condensation free.

I found this reference to kneeling and sitting on fabrics at an REI website;

"One rainwear manufacturer calculates that a 180-pound person exerts about 16 psi when kneeling and 8 psi sitting. Accordingly, it uses fabrics that offer a minimum rating of 20 psi.

REI's Nagode contends (and Gibson concurs) that such claims have never been supported by hydrostatic resistance testing. In the marsh/wet-rock/backpack scenarios mentioned above, the pressure created by the actions described simply displace water away from the fabric. "The water would need containment to generate pressure," says Nagode. Everyone agrees, meanwhile, that 3 psi is more than adequate resistance to repel rain."

I found this at Wikipedia; "One specific definition of "waterproof/breathable" requires the fabric to withstand over 1,000 millimetres of water (9.8 kPa) pressure without leaking (see hydrostatic head)[citation needed].

These values should be taken with some caveats. Rain room tests show that some fabrics with less than 1,000 mm of water resistance keep water out sufficiently for practical purposes. Garments made from these fabrics tested in the Leeds University Rain Room show no signs of leakage after 4 hours of heavy simulated rain, 5 times heavy British rain."

Further research tells me that the largest raindrops fall at a maximum speed of 20 M.P.H.

The British minimum standard for waterproofness is 1000MM and that is good enough, I have read, to withstand rain driven at 35 M.P.H. What does that tell us? It's close to saying that fabrics at half the British standard can repel rain and be waterproof. I wonder if some people realize that 1000mm is like hanging a meter long stuff sack with water and expecting it not to leak. 422MM is still about 1/2 that. Like everything in our culture, standards tend to be over the top, like the amount of detergent we are supposed to wash our cloths with!

"Rain room tests show that some fabrics with less than 1,000 mm of water resistance keep water out sufficiently for practical purposes."

This does seem very logical considering the fact that people used to use materials that could hold very little water, but worked fine as a shelter material.

The one problem with this discussion is that a lot of people are misreading it to think that cuben shelters are going to leak.
A high percentage of these people will start thinking that the normally occurring condensation is now suddenly water leaking through their cuben fabric.

Hi Dan

What Richard wrote was:
> This means it would serve well as a sail but it is a poor solution for heavy rain protection.

What you wrote was:
> I would do this especially before declaring that this weight of Cuben is worthless for rain protection.

(My italics) I see a very big difference between saying something is a 'poor solution' and saying it is 'worthless'.

> the first thing I would have done after being shocked would have been to actually test
> the tarp to see if the HH reading I got had any relevance to actual performance.
Sounds like an excellent idea to me, but there is a small problem. Half a dozen of us can repeatedly measure the hydrostatic head of different samples of the same weight of Cuben Fiber fabric and expect to get very similar results. That gives the metrology some respectability. There is then an expectation that if another person were to do the same test they would get very similar results.

But just how does one measure the performance of a tarp in the field in a manner which can be repeated many times by many people in different places, while giving a numerical result? Just using the tarp once or twice and saying it did not leak is hardly a reproducible test.

Is there a 'Cubens Proprietory version of mylar'?
No. Mylar is a registered trademark owned by Dupont Tejjin Films for plastic film or sheet made from Polyethylene Terephthalate (PET). It is not like PVC, which can have a huge range of different plasticisers and fillers added to get a wide range of physical properties. Cuben can have no proprietary ownership here. Also, the properties of Mylar are very consistent.

Mind you, other companies do produce the same film (chemically speaking) but give it different trade names. Patents have a finite life. Given the relatively small amount of Mylar film used by Cuben, I doubt that anything is made specifically for them (alone) though.

> has BPL or anyone else concluded what misting is or is the jury still out?
Most misting is due to condensation being knocked off the underside of the tent fly fabric. It is possible that in some cases water may be forced through seams if they have not been sealed. In a few cases where the HH of the fabric is very low and the rain drops are large and travelling near terminal velocity, some water may be forced through the fabric as well, but this is fairly uncommon.

However, I am sure the argument will rage for a decade (or more) to come! :-)

Cheers

Hi dan again

> I'm curious what you mean 'the way the mylar bonds to the spectra'.
If we look at Cuben Fiber fabric we see two layers of Mylar bonded together with a scrim of Spectra or other synthetic fiber in between. The synthetic fibres used are fairly hard, unlike (say) nylon.

Now, somewhere along the line the two layers of Mylar have to be pressed together very hard to get the intimate bonding used. One would expect a big press or rollers to be used. But that means that the Mylar film is going to be under a very high pressure. In some places the total thickness will be that of two Mylar films. In other places the total thickness will be that of two layers of Mylar film PLUS two layers of very hard Spectra thread.

Now, right where the Spectra threads cross over the pressure on the Mylar film during bonding may be sufficient to thin it further or to weaken it. The very hard fibres could retain full tensile strength, and the Mylar film could retain what appears to be zero porosity when measured on an air porosity test apparatus, but it might well leak drops of water when tested on a Suter (HH) tester.

I don't know this, but I can see it as being a possible explanation for what has been observed and measured. (FYI: I spent 27 years in textile research as a lead scientist.)

Cheers

My comment on the durability of mylar in comparison to nylon is based on real world experience in using it for: molding, vacuum bagging, RC airplane covering. IE running it over corners, wadding it up, pretty much not paying much attention to it like I do to nylon bags.

Its not bad like acetate for tearing/brittleness. In fact, its pretty decent for bending and folding. Just not up there with nylon. It also depends on the thickness of said mylar(duh). Probably also depends on how highly polymerized said batch of mylar is or cross link polymerized it is. I forget how much cross linking is going on. Could be none and I don't feel like looking it up. If you really want to know open your trusty plastics materials handbooks. The good ones are larger than the normal materials(steel, bizimuth, etc) handbooks as there are so many varieties of every conceivable plastic out there.

For this discussion, I think we can assume that Cuben Tech folks aren't idiots, and got their mylar properly polymerized to their desired maleability and tear strength criteria. Though in this case their polymerization criteria has far more to do with bonding the dyneema to the mylar I would presume, than say maleability(waddability)

After all space suits use mylar to maintain air pressure inside. Though I think this is layered aluminized mylar as coating mylar with an aluminum coating is for that needed extra real air permeability of 0 is fairly easy due to its high electrostatic properties compared to other plastics.

Also mylar has that nice property of shrinking when heated, creating a bunching effect of the dyneema between the two layers. At least this is what I am assuming they are doing. Once again said shrinking property of mylar is dependent IIRC on how much polymerization is done on said mylar to begin with.

I have had RC(Radio Control) mylars that literally fall apart if you run them over even a slightly sharp edge or crack and split. Others you can munch/bunch them a bit, but it will leave crinkle lines. For this reason when molding you you have to have no sharp corners on your molds. On certain types of nylon, you could literally have a knife pointing straight up and the nylon bagging material would form around it without a hitch. Try doing that with your aluminized mylar balloon. Not a chance.

Long way of saying, that for Cuben Techs products, they probably don't give a hoot and a hollar about wadding up their products. Sails are NOT wadded up in a bag, well some folks do… Not their racing sails! They are generally ROLLED, or at worst folded loosely creating no sharp points/lines. In other words their specs for polymerization of their sails could probably be far looser than that wanted for stuffable tents/ground sheets you name it. It could simply be a bad batch on the edge of their specs perfectly OK for sails on a boat, but not all that hot when it comes down to waterproofness.

Sorry Roger, though the name Mylar is trademarked, it can actually have a wide range of material properties and lets not get started on what happens when additives are introduced into the discussion! Its kinda like talking about nylon in that regard from what I have read about it and from my user end experiences with the stuff.

<< Proud owner of several silnylon products that produce condensation/water seepage >>
<< Yes, I have wiped down my fair share of tent walls of said sil/nylon product >>

The UL version of Cuben fiber has only leaked relative to accepted standards of waterproofness. It did not leak relative to HH figures Cuben has supplied to anyone. As far as I know, Cuben has not supplied any numbers. So, to say it leaked is inaccurate.

Roger, you said; :"Sounds like an excellent idea to me, but there is a small problem. Half a dozen of us can repeatedly measure the hydrostatic head of different samples of the same weight of Cuben Fiber fabric and expect to get very similar results. That gives the metrology some respectability. There is then an expectation that if another person were to do the same test they would get very similar results.

But just how does one measure the performance of a tarp in the field in a manner which can be repeated many times by many people in different places, while giving a numerical result? Just using the tarp once or twice and saying it did not leak is hardly a reproducible test.""

I have said a number of times that what it does in the field trumps what it does on a tester. What you are saying is that if 20 different testers get a 422mm rating, then we should not expect it to perform in the field and shouldn't bother trying it. This is why Richard so clearly came to the conclusion that he should return his MLD tarp without ever really trying it.

Roger also said; ""(My italics) I see a very big difference between saying something is a 'poor solution' and saying it is 'worthless'.""

Sorry Roger, there are many that would disagree I'm sure. In terms of what people are interested in, it would be difficult to accept either.

Brian, thanks for that info, it's very helpful.

Roger,

It's also quite a leap to try and analogue a suter test to a rain storm. Even if it may "statistically" equate.

A clamped piece of non-stretch film reacts completely differently than a dynamic (no matter how tautly "pitched") body of a tarp or shelter.

I'm not arguing with the numbers, but personally, I think they're irrelevant. The flow rates seen look completely expected to me. Once the mylar is compromised, that's it. In the end, the stuff works, and laboratory testing procedures, as much as we always *want* them to be the definition of reality, only ever portray the smallest piece of the infinitely complex puzzle.

Anyway, I'm admittedly skeptical of these precise testing procedures being extrapolated into broad strokes, in all fields, but I'd be much more inclined to be interested in the data using a test that involves accelerated drops of water, since that's what rain is. Suter testers seem more relevant to figuring out how well a tarp will do under a waterfall.

Steven,

You said, "Rain room tests show that some fabrics with less than 1,000 mm of water resistance keep water out sufficiently for practical purposes." This does seem very logical considering the fact that people used to use materials that could hold very little water, but worked fine as a shelter material.

The quote you used is most typically sourced from http://en.wikipedia.org/wiki/Waterproof_clothing. In turn that article's relevant information is sourced from tests paid for by Paramo-Furtech-Buffalo . The tests were conducted in the Leeds University Laboratory.

The original marketing report, before it was edited many times to the current versions found on the Web, began by saying:

“International standards for waterproofing state a minimum of 150cm hydrostatic head. (1,500 mm) Feather and Fur type garments don't pass this standard but do remain waterproof in heavy rain as demonstrated by the Leeds University Rain Room Test and vast amounts of users, including Mountain Rescue Teams, the Search And Rescue Dog Association and numerous guides and outdoor instructors.”

The original marketing report never listed the rain head height or the max drop sizes so you could do physics calculations to determine the kinetic energy the garments were subjected to. By what is a REALLY IMPORTANT THING TO TRY AND UNDERSTAND is that these garments all had thick fleece linings backed by a rigid body surface. The Impulse-Momentum form of Newton's Second Law can make rain drop force as little as you need to market your garment as waterproof by just increasing the fleece thickness.

So my Pertex Equilibrium over 3/4" (?) Pile should do well in heavy rains because of the "shock absorption" of the pile?

or

Equilibrium is just ok so they backed it with soft stuff to make it more water-resistant?

In either case it should be good with heavy rain, correct?

So Richard measures the water pressure rating (HH) of some Cuban Fiber fabric and finds it's low. I assume no-one is going to argue with his figures?

On the other hand, as one of our readers emailed me privately (thanks), we have companies claiming as follows. My italics.

---

Cuben fiber is lightweight, highly durable, and is 50-70% lighter than Kevlar, four times stronger, and allows flex without losing strength. It is also less than half the weight of silnylon, has low specific gravity (floats on water), high chemical resistance, excellent UV resistance and is 100% waterproof.

---

Cuben Fiber is fully waterproof in hard rain…
Cuben Fiber 1.2oz sq/yd – Totally Waterproof – Very Strong- Very Light

---

Cubic Tech's new CTF3 "max light" series of non woven laminates making it exceptionally waterproof, dimensionally stable, and of course gossamer light. All of this means you can have confidence that your shelter will keep you dry, won't need re-tensioning in the middle of the night and won't take up much space in your pack.

---

Now, I don't want to name the companies because I doubt they knew just how low a rating the thin versions of the stuff really have. But maybe Richard's measurements should encourage a small change in the marketing spin? Clearly the stuff is not totally waterproof.

Does that mean Cuban Fiber should not be used for a shelter? I never said that, and I don't think Richard did either. I imagine it could be used in mild conditions very happily, although I think we need more information about lifetime and rate of degradation.

Cheers

As far as I can tell, a hydrostatic head of 422 means that particular Cuben Fiber, if fashioned into a stuff bag 16.5" tall, it would hold the water if filled and hung up. That sounds pretty waterproof. What I find amusing Roger is given that, you are arguing against it's usefulness in UL packing for tarps, ponchos, raincovers, and many other practical things based on standards that, by the nature of standards, are in excess of what is needed anyway.

I think a more practical way to approach this would be to find out what the minimum fabrics are that do the job we want them to, and then find out what the HH figures are for those. It seems that much of UL packing has to do with risk assessment so I don't understand your resistance to seeing different meanings of what waterproof can be. This is the practical way to go about things. What is showing here is how limited things can be when we accept standards somebody else set up that we do not question.

We need more information about lifetime and degradation of many fabrics. Most of them get wasted by UV alone, and in that sense I'm willing to bet Cuben has done it's homework.

I agree with Dan Mchale, hyrdostatic head numbers NEVER translate into real world performance. I have been using one of my CT2K.08 9'x9' flat tarps for over two years now and never once has it ever "misted". At .75oz no other material can compare. Cuben Fiber is super strong, amazingly lightweight, has amazing tear resistance, doesn't absorb moisture, has awesome UV resistance, and is one of the most real world water resistant material available.

"As far as I can tell, a hydrostatic head of 422 means that particular Cuben Fiber, if fashioned into a stuff bag 16.5" tall, it would hold the water if filled and hung up. That sounds pretty waterproof."

How does this test water that is moving at speed, i.e. water pressure? A simple DWR could handle that.

I too would like to see additional testing, but regardless of the results, I'm still going to be using cuben fiber for my shelters whenever I can afford it.

David, from information from an earlier post I made, I passed on that the minimum British standard for waterproofness was 1000mm and that rating could handle rain wind driven to 35 MPH. The maximum rate of falling rain is 20 MPH so using these numbers we need about 571mm to handle 20 mph rain. 15 mph rain would need 429mm. We don't really know how that was determined in the first place though, that 1000mm, so we're in the same ball-park with 422mm – Richard's test number. If that 1000mm came from the same place that brought us ' a pound on the foot is 5 on the back' we can probably add some NaCl to it and call it a day.

Did you do your homework yet and test your Cuben bags? I just hope the seams are well sealed in order to hang water.