Cuben – The 422 mm hydrostatic head dirty little secret

[dan mchale]

No I have not. But what are we comparing the light cuben to that can compete with what it does? I'm just repelled by the attitude of the OP. He does jump to serious assumptions regarding condensation V leakage. At some point, when you are dealing with such light fabrics, compromise has to become an issue, and then its other qualities come into play. Just what are the credentials of the OP to go around defaming companies with such little relevant testing?

He even applies his experience with silnylon as though that applies here. Aren't people aware that the silnylon that is available to reputable manufactures is vastly different that what is dumped on the DIY or MYOG marketplace? There are too many generalities being made here.

Greg, considering the scale of the fabric you tested, How relevant is your test that you describe with heavily used lightweight Cuben? I can understand the dissappointment in discovering that no miracle occured in the test but if something is working…… How would you react if somebody came up to you and squeazed your neck until you died? What relevancy does that have as to what you do in your life? Did your tent Cuben leak during use? There are tests to see wether a plant is still alive also. What you do is pull it out by the roots and take a look.

[Greg Mihalik]

Dan,
There have been long discussions regarding the "misting" of silnylon. Then Cuben came along, a strong, "impervious" laminate, which appeared to be the holy grain of "light and waterproof".

Now, testing shows that there "may" be some issues with durability. More testing is needed, and as the OP states, on multiple samples, by multiple testers.

I have not seen any "defaming", only "this is what I saw", and "this is my choice". And when it comes to data, testing, and integrity, the Richard N. will get my vote every time.

I agree that Cuben seems to be the best choice for lightweight shelters. I've voted with my wallet, big time, and recently placed yet another order. But I really want to see how the numbers play out. This is an emerging technology and bumps are to be expected. The question is "How big is the bump?" We won't know for a while, but until then, I suggest we can collect empirical evidence in this new light, and then put it all together.

[Greg Mihalik]

Dan,
I missed your edit and the added question –

"How relevant is your test that you describe with heavily used lightweight Cuben? Did it leak during use?"

"Leaking" wasn't expected, looked for, or found on the trail.
"Cuben doesn't leak. Must be condensation. No big deal."

When this issue came to light, the quick and dirty test was performed. Relevant? Only to the extent that it seems to confirm that, in fact, the impervious Cuben did leak. No indictment. Just another observation.

There won't be a quick answer here.

[dan mchale]

"Unless Cubic Tech or Mountain Laurel Designs can solve the problem with the poor hydrostatic head performance of my MLD Cuben Grace Duo I will probably never buy another Cuben product."

The above quote may not be defamation but it's certainly off. I have no problem with him being dissappointed in the hydrostatic head numbers. It's possible that the hydrostatic head test has little relevance in this industry, unlike industries like firehose manufacturing. It is possible that companies are competing over numbers that are irrelevant. I think it's silly when there are other factors that are more important in any fabric, like the Longevity of the waterproofness and actual strength of the fabric. When it comes down to it, it's just a lightweight plastic tarp, and it's the best of the bunch so far.

This is what you say Greg, and you are falling into the trap as well;

""Leaking" wasn't expected, looked for, or found on the trail.
"Cuben doesn't leak. Must be condensation. No big deal."

When this issue came to light, the quick and dirty test was performed. Relevant? Only to the extent that it seems to confirm that, in fact, the impervious Cuben did leak. No indictment. Just another observation."

The CUBEN did not leak in use. It only leaked in an irrelevant test for a Number that has been thought to have some relevancy in the industry.

[David Ure]

"I'm doing some what I would call real world testing of some heavier Cuben today, fabrics in the 4 oz/yd relm. I think in general, we will discover in this current post, the irrelevancy of the hydrostatic testing for these applications. "

4oz > than 0.74oz. I would expect a HH of about 1800 mm. Functionally waterproof. Unless you are testing the fabrics used in UL tarps, why bother. No one is going to make a tent out of 4oz cuben.

[dan mchale]

It's all relative David. When I can literally rip the mylar sheets that make up cuben fiber apart from each other and they are still waterproof, it has relevance. Like I said, What are we comparing it too and did Greg actually have a problem with his own tent? Ultimately, this will be about whether the test is relevant. I believe there can be a waterproofness that is completely adequate under actual use conditions that might fail in some silly comparison test for pressure. Lets test cuben fiber for the toughness of its waterproofness compared to other fabrics. Perhaps that might be more important. Just maybe we are at a point in fabric technology where we can see that there are other properties more important than this hydrostatic head thing and that it is apparent to me at least, that hydrostatic head is completely irrelevant beyond a certain point in the applications we are talking about. Imagine how important hydrostatic head can be when considering diving equipment – like in bouyancy regulators. There it has relevance, while here it is of very limted value.

[Greg Mihalik]

Guess I wasn't clear –

"I have had a personal communication where it was possible to squeeze water through a lightweight cuben tent body that had seen many nights of use."

I have Communicated with someone who did the "squeeze test".

I have not had any problems with Cuben shelters. [Though I wasn't looking either ;-)]

[David Ure]

And to add, obviously shelter design – panel angles, sections, etc – and the direction of the rain, size of drops, etc – will make a big impact as to whether the shelter can withstand the water.

But I do think the thickness of the fabric will make a difference when subjected to water pressure. No?

[dan mchale]

of course David. I said it's relative. Obviously, the thinner a fabric is, the easier it will be to blow things through it under pressure – so what, when those pressures are rarely found in practice? A rain drop does not exert constant pressure and it does not exert it over a broad area constantly. What are we comparing the fabric to? There is NOTHING to compare it to. Cuben is the best plastic tarp going. It's the ultimate fantasy. I had to laugh at Boeing for trying to market a Carbon Fiber plane to the public as 'plastic'. I'm glad they dropped that non-sense. They must have gotten a lot of Flak for that!

Now I see that the test Greg mentioned was something he heard about. There is not even first hand experience there. It is completely anecdotal and we have no idea of the amount of pressure applied.

[Roger Caffin]

Hi Dan

Forgive me if I am wrong, but you seem opposed to lab testing and scientific evaluation for some reason. Is this really so? Hopefully not.

> Obviously, the thinner a fabric is, the easier it will be to blow things through it under
> pressure – so what, when those pressures are rarely found in practice? A rain drop does
> not exert constant pressure and it does not exert it over a broad area constantly
I am not sure what you are trying to say here. But one thing I can tell you is that the pressures being quoted ARE found in practice, frequently.

For a simple start, groundsheets can be subjected to very high pressures when you kneel on them on hard ground – or worse still on sheet rock. They need to handle pressures well over 40 kPa at times. Those can be over a significant area and for a significant time.

But more interestingly, we are starting to find from the published research literature that the pressure exerted by large raindrops can be a lot higher than we had previously thought. This has caught me by surprise too. The time that very high pressure is exerted by a single raindrop is short, but it is of concern.

I don't think that doing a scientific evaluation of fabrics and finding that some popular ideas are wrong is anywhere near the same thing as destructive criticism of manufacturing companies. If anything, I would hope that the testing being done may prove to be of real value to the UL cottage industry – even if some cherished ideas are shattered in the process. And remember: we are setting up to duplicate the research, as is ALWAYS done for scientific research.

Cheers

[dan mchale]

I am opposed to hystreia and jumping to conclusions. Why would I be opposed to lab testing? I just got through describing that I disassembled some Cuben Fiber and tested the components for waterproofness. Does that sound like I'm not into lab testing? I'm afraid you have not really digested what I have said Roger, but are rather jumping to conclusions yourself about me. And it is a TARP that Richard suddenly has to get rid of. It has no floor. I seriously doubt that MLD has experienced problems of waterproofness with it's clients and do believe this post was started with a bit of unwarrated hysteria. Sure, it's nice to know how all the different fabrics compare hydrostatically, but like I said, I think we will find the real relevance of the importance of it. This of course will be found out scientifically. In the meantime I am voicing that I think the conclusions of the OP are non-sense and do hurt the parties in question.

This is what the OP said in his first post; "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."

There is no way that tarp is any less suited to heavy rain than any other and part of my point is that perhaps field testing will show that more than a miss-applied testing device. Anyone that has used Cuben Fiber knows this is all bunk and no amount of measuring hydrostatic head will determine the suitabiltiy of Cuben in the field, when that suitability is determined by comparing Cubens HH with other fabrics.

I am simply questioning his overbroad and rushed conclusions. I'm all for shattering cherished beliefs but it is difficult to tell which ones you are referring to. I even mentioned compromises we make when using UL gear, but maybe you missed that also in your speedread to judgement. If Richard was any kind of scientist he may have questioned his own cherished beliefs before coming to the conclusions he did. Obviously there is a disconnect between what Cuben can do in the field Vs how we compare it to the cherished belief we have in the meaning and relevance of HH. I dare him to get rid of his Cuben tarp and then even think he can duplicate what it can do with a siltarp or any other tarp.

[Sam Farrington]

It is understandable for folks whose livelihood is related to these issues to get a little worked up. For the rest of us consumers less is at stake. Perhaps only the cost of a few purchases of equipment, or materials in my case, and some uncomfortable experiences if and when the equipment fails.

But it is also important for vendors to understand that we consumers have profited greatly from Richard's posts for a long time. True, his choice of language was not as restrained as usual. Obviously because he was truly surprised. I know I was.

Extensive testing of samples is not going to relieve this surprise. When a few samples do poorly when tested, you have a baseline that raises legitimate concerns. How can one be sure that their next purchase will be that much better than the baseline. In the current circumstances, one can't.

For example, when testing carbon shafts, I stopped testing after a poor test result, because if one or two fail, there is a greater likelihood that more will fail. But when a shaft tested well, I retested at least twice more to see if the good result would be consistent for that product. Needless to say, the ones that performed well for three or four tests are the ones I'm using for tent poles. Maybe that's not 'scientific,' but it was the least expensive way to make choices for myself and friends.

I've been burned more times than I can count with materials failing, and so have a very low tolerance for hot air from vendors. But I've followed Richard's posts long enough to have developed a good measure of trust in what he has to say.

I don't get what the chat about condensation was all about. Red herrings, maybe? This isn't about condensation, it's about leaking. What's the point of busting a gut to design a shelter with the lowest condensation, if the darn thing is going to leak anyway?

[ziff house]

Bad logic, the fact that you are subjecting a fabric to a high point pressure with an object is irrelavant as the water presure on the other side would still be zero. But you would likely creat a hole in cuben as i have done, So DON'T DO THAT!

[ziff house]

is a good example of why this threads headline is injurious to many. Although Richard has in effect pointed out that his finding has little real world meaning.
I my life i have used for years a silnylon tarp, then a montbell tent with a skookum PU fly. I can't think of any difference between them in terms of water management. THE most critical factor in tent design is keeping distance between inner and outer tent [bivy functions as inner].

[dan mchale]

What was that you said Samual; what's the point of making a shelter waterproof when it's going to condense anyway?

[David Ure]

"I dare him to get rid of his Cuben tarp and then even think he can duplicate what it can do with a siltarp or any other tarp."

Dan, do you mean with respect to HH? If so, Richard has tested that as well – at almost 3 times the HH of the cuben sample he used.

[dan mchale]

No David, in terms of real world performance. I already made my point that in this case and probably many more, excessive HH is of little importance. Like Ziff so eloquently said, keeping the tarp off yer body is sometimes the most important thing. I meant duplicate in terms of the entire performance of the Cuben Tarp; strength, ability to achieve and maintain tautness, AND waterproofness. Again, my point is that excessive HH does not trump these other factors in the field, and it's relatively low HH does not mean it won't keep the rain off.

I did not catch Samual's title Ziff – pretty funny. People probably get tired of hearing about Cuben Fiber. I don't sell it so have little at stake. I have worked with it quite a bit and know what it's about though. This is an interesting subject and apparently this level of Cuben is probably the only with a low HH if the figures are correct, and this community should understand the nature of compromise when pushing the extremes. I think it will be born out that there is little or no compromise here, though, and peoples cherished beliefs will break down a little regarding the overall importance of high HH values.

[BPLwiia]

How many samples of Cuben fiber/material were tested by the OP? Wasn't it just one? Wouldn't someone test extensively on multiple samples, if not many samples, before coming to a conclusion based upon one test?

[James holden]

what id like to know is whether anyone has had any issues with their cuben or silnylon bivy bottoms or ground sheets … id hate to wake up in the middle of a puddle … not to mention those parts probably see the most wear n tear

if there are a few more "condensation" drops going drip drip drip drip … no big deal … people will just come on BPL asking about it, and well just tell em its "condensation" ;)

[Sam Farrington]

Dan,
Both the name and the point backwards. Oh, well …

[Rob Vandiver]

Qualification: I am certainly not a scientist. Also, I have no cuben products simply because I cannot afford them at the moment. I have looked dreamily at the weight differences, but the $$/Oz doesnt make sense for me either – there are better things to get.
I have read repeatedly that while tarping it is imperative to choose your site well. One of the things to look for is loose soil or pine needles, so that any moisture has an escape route.
Are there any ground cloth or tent floor fabrics that can withstand the 40kPa of pressure you are talking about? Are there any UL solutions?
As for the tarp itself, with nothing but the force of the raindrop itself, what would be an acceptable HH number to be considered waterproof? Looking online I see no clear definition, with the range anywhere from 1.5K to +10K.
Also, at what point does the "misting"/"condensation"/"leaking" become unacceptable? if the majority of the drops are running down the sides of my tarp, with a few drops hitting my bivy, am I even going to notice them, especially if I am getting some spray from the ground?
I think threads like this are what make this forum so great: new information comes up and there is lengthy discussions about the end results. We need the science to tell us concrete numbers: much like EN ratings of sleeping bags. Like the bags, though, it is up to the end user to figure out what is within that particular person's comfort range. I just hope that no one is automatically swearing off cuben or regretting the purchase of an expensive piece of gear even though it has worked fine for them.

[Dan @ Durston Gear]

"what id like to know is whether anyone has had any issues with their cuben or silnylon bivy bottoms or ground sheets …"

This is entirely anecdotal and no substitute for scientific testing, but over the past two winters I've camped on snow four times. 3 of those 4 times the floor leaked and the only floor that didn't was 1.51oz cuben.

1 night x 3000mm PU/nylon floor (Marmot Tent) = Leaked from knee pressure etc.
2 night x 1200mm Silnylon (Snow cave w groundsheet) = Leaked from knee pressure etc.
1 night x 1.51oz (CT5K.18) Cuben (HMG Echo I) = Performed perfectly

[Roger Caffin]

Hi Dan

Perhaps we are not talking about the same things here? You seem to be focused on actual tarps and tents in the field? That's fair enough of course.

But 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 that the fabric has a far lower pressure rating than any of us would have expected.

Is a hydrostatic head relevant to field performance? Most of us science types think so. But that is secondary to what was the issue here: that that particular weight of Cuban Fiber fabric had a much lower pressure rating that we had been expecting. Here we go from 'belief' to 'measurement'.

Cheers

[Brian Austin]

What is germane to this discussion, is that no matter which way you turn, mylar will always have a far shorter lifespan than nylon and polyurethane or silicone. Thus, why mylar will leak sooner than the others. You can't bend/stretch mylar nearly as long as nylon. Nor does it like to be folded. Anyone who has done vacuum bagging knows this as is the natural progress is that nylon bagging material is expensive and mylar is cheep. Except mylar doesn't go around a sharp corner nor does it last all that long.

That is where the leaks come from as the meat of the fabric, the UHMHDPE while waterproof, does not cover 100%. I would bet that the higher thickness cuben fabrics are better in this regard though. If you want durability you are talking nearly any plastic OTHER than mylar. And like all plastics there are many grades of stuff called "mylar"

[James Marco]

"Is a hydrostatic head relevant to field performance? Most of us science types think so. But that is secondary to what was the issue here: that that particular weight of Cuban Fiber fabric had a much lower pressure rating that we had been expecting. Here we go from 'belief' to 'measurement'."

Absolutly. That is what science is. Typically, we bring up more questions than we answer, though…exactly as has happened here.

Is a hydrostatic head relevant to field performance? (Roger's question.)
How much water resistance is expected? (1500-10000?)
What conditions should be tested for? (used, new, interior wetness, humidity levels…)
What is the impact strength of a rain drop? (pitch angle, tautness, length of a rain drop, shape, terminal velocity, wind strength…)
And a lot more.

This is all quantifiable data. We can put numbers to it, or, the so called hard science.

The second component of science is qualtative. Often we get numbers that have no real world validity. A HH of 50000mm means nothing iff we only need 500mm. Building a tower to support a load of a ton, means nothing if a child is playing with blocks. How can we asses a persons psychological state with numbers? Yet we accept psychology as meaningful. Enough/not enough… a binary state, yet we accept computer science as a valid science.

Simple measurements are often not enough (apparently, Dan McHales point.) Nor do we have enough duplicated data on HH to say one way or the other. I will simply wait for more quantitative results from the HH testers, for now. And, try to put this together with qualitative data from the field testers results.

Both sides of the coin are equally valid. Yet both describe the same coin.

The low HH values of cuben are indeed surprising. The effects in the field have been noted with the failures from various companies to adopt the fabric, more than the expense alone would seem to dictate. Perhaps not directly related to the HH, but it seems to be an important component. Hilleberg, Exped, MSR, etc do not use cuben.

[Author]

Posts