Cuben – The 422 mm hydrostatic head dirty little secret

[Richard Nisley]

John,

There are three general styles for Tyvek: 10, 14, and 16. Under each major style there are many sub styles with unique specs for each. I purchased two Tyvek groundsheets many years ago. I don't think either retail source said what style they were but I figured it out by comparing each to the specifications after I purchased them.

One of my Tyvek ground sheets is a soft Style 1422A material. It is spec'd by DuPont as having a hydrostatic head of 40" H20. After 5 years of use and multiple washings it now tests at 33" H2O which is equivalent to 844mm H2O and is double what my new Cuben MLD Grace Duo tests.

My other Tyvek ground sheet is a hard Style 1079. It is spec'd by DuPont at <15" H2O. Mine currently tests at 11.07" after five years of use. I quickly figured out it was useless as a ground sheet. After that I used it to put over my sleeping bag when it was raining hard. DuPont does not list the air permeability for this type of Tyvek. It currently tests .69 CFM on my equipment and this puts its close to the new .5 CFM Polartec NeoShell.

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. I still have a couple of Granite Gear Cuben dry bags. Sometime before packrafting season I will test them to see how much at risk I am using them.

[James S]

Thanks for the information, Richard!

[Anonymous]

Considering and digesting this for a few hours since first reading the thread, it would seem that if these test results were indicative of the true character of cuben we would have had some experiences reported by now. This material has been in use for quite a few years now and I have not read of any users complaining of the leakage. If Richard tests applied widespread to common material used in the shelters this would have certainly come up before now. So this would seem, based on common experience alone, to be just a bad sample Anyway, I hope this is the case since I just ordered a shelter a few weeks ago and am waiting on delivery.

[Richard Nisley]

Ben,

The hydrostatic tester head is a 5" diameter circle. As the pressure builds, some additional fabric can be pulled into the convex pressure area. I only need two scraps each of which is a minimum 6" long for the shortest axis. One piece should be virgin material. The second piece should be preconditioned to simulate a summer’s use for the second hydrostatic head test. Label each piece with a magic marker. I don't need to know which piece was conditioned. I will just report the results for each labeled piece.

In this prior thread I pointed out the fast degradation of silnylon from merely stuffing and un-stuffing it: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=43902&disable_pagination=1 the same type of thing may or may not happen to Cuben.

Subsequent to the above thread, I found an article discussing a test procedure that a European fabric manufacture uses to anticipate how their fabrics will behave with use. The graphs are below. In summary you can put the second scrap sample perpendicular to a strong fan and let it flap for 90 minutes or just wash it, without soap, 8 times in your washing machine. This will give us a good idea if there is rapid hydrostatic head degradation of Cuben during the course of a summer’s use. Only their sil/PU material didn't quickly degrade with use, but as David Olsen of Oware pointed out in another recent thread, there are a lot of different sil/PU formulations.

Send me an email through the forum and I will give you the address to ship the Cuben scraps for testing.

[Roleigh Martin]

What is the thickness of the Cuben Fiber in question? Can it be described in terms of how Cuben Fiber is described at zpacs.com 's materials page?

Anyway, this is another very interesting You Tube Video of how well a zpacks cuben fiber tent did a super strong thunderstorm in the Appalachian trail as a real world positive note counterpoint:

http://www.youtube.com/watch?v=LLqfol0IU3s&feature=related

He has the single person variant of the tent, I have the double person variant of the tent

http://www.zpacks.com/shelter/hexamidtwin.shtml

This is good. It handled that horrendous downpour just great.

Another question. what if a person created a double wall cuben fiber tent, under a super prolonged jungle forest rain, any penetration of the outer wall might fail penetraing the inner wall. Imagine one of Joe Valesko's cuben fiber tents with the insect netting as the inner tent and as the outer tent the same tarp without the insect netting. The combined tent weight would still be under 1.5 lbs so definitely lighter than ny single wall "absolute waterproof" nylon/pu coated tent.

Bottom line, what counts is how well the tent does in torrential rain storms — if they continually do well, well what is there to complain about?

[David Ure]

How long was the 'thunderstorm'?

[Richard Nisley]

Diana,

I won't embarrass you by asking your size and weight; I will just provide you with the pressure values for my size 5’11” and weight 190 lbs. Keep in mind the Cuben used in the MLD Grace Duo will only handle a maximum static force of 422 mm H2O.

– Laying on my side, I exert 232.07 mm H2O.
– Laying on my back, I exert 119.35 mm H2O.
– Kneeling on both knees, I exert 12,953.53 mm H2O.
– Once uniformly positioned on my butt, I exert 2,428.79 mm H2O.
– As I attempt to get seated I exert a brief force (do to uneven positioning) of 12,143.93 mm H2O.

[Aaron Reichow]

@Roland

I don't think anyone is complaining so much as trying to suss out fact from the assumptions made about cuben. If it takes a double wall design to make a decently waterproof tent out of cuben, then how much has really been accomplished? My one person double wall tent manages to weigh a little less than 1.5 lbs, despite of it being made of 30D and 70D silnylon rather than cuben. Just a thought…

[Jeffs Eleven]

So is that 12,953.53 mm under each knee?

[Diana Vann]

It would not have embarrassed me, but it's probably a good idea not to set a precedent.

I'm 5'7", and a normal weight for my height.

[Richard Nisley]

Lance,

Water resistance can be measured by two different methods. One is the low hydraulic pressure test, JIS L 1092 A/ISO 811. This test is used to measure water resistance up to 2,000mm, approx. 3 psi. The pressure gradient for this test is 600mm pressure rise/minute. This test is commonly called the “water column test” and can simulate the pressure applied by a column of water up to 6 feet high.

The second method is called the “high hydraulic pressure test”, JIS l 1092 B. This test is used to measure from 2,000mm to as high as 30,000mm. The pressure gradient for the test is 10,000mm pressure rise/minute.

Each method uses different equipment to measure water resistance. Both methods apply pressure, by water, to the fabric until the fabric begins to leak. In both tests you don’t consider it a leak until there at least 3 distinctly different drops coming through the fabric

The primary difference between the two methods is the rate at which water pressure is applied to the fabric. Many technicians feel that exposure to the artificial situation created by machines is not realistic after the fabric has been on the machine over 3 minutes. Therefore, some testing may require a wire mesh screen to achieve a more realistic testing situation.

The maximum pressure I use to test silnylon or Cuben is 3,515 to guarantee no fabric damage. At this low maximum press no screen needs to be added over the fabric. In addition, my tester has a metal bar that levels-out any pressure bulge.

[Richard Nisley]

Roleigh,

Thank you very much for taking the initiative to get Cubic Tech involved in this discussion. For your information I also sent them an email soliciting their participation via '[email protected]' with the thread URL when I initiated this forum thread.

[Lance M]

Richard, thanks for the info on HH testing methods.

[Richard Nisley]

Roleigh,

Q – What is the thickness of the Cuben Fiber in question?
A – .05 mm avg.

[Richard Nisley]

Jeff,

Yup!

[ziff house]

would say everyone is going to get way too persnickity about this. Lets face it, if you are faced with days of rain in the bush everything gets damp no matter what. Theres condensation. [no matter what, ventilation will just let the mists in].then water comes in with you, etc etc. My own limited experience so far is its waterproof, and i have yet to hear any real world complaints.

[David Ure]

"My own limited experience so far is its waterproof, and i have yet to hear any real world complaints."

YMMV – obviously. But there are some real world complaints if you search. I think you qualified this comment correctly by stating 'limited.'

Looking forward to more tests.

[Anonymous]

Do you have some links readily available David? Would appreciate it. Even though I have already ordered, I would like to make some judgment on the confidence that can reasonalby be placed on the use of this product. Henry Shires stock and business acumen is rising by the hour. He was outspoken a couple of years ago against the hue and cry for him to make some of his shelters out of cuben.

[Dan @ Durston Gear]

Somethings not right here. I think we should hold off on judgment until a few more samples have been tested and in a few different weights.

Even if CT2K.08 (0.74oz cuben) proves to have a much lower HH than thought, I still hypothesize that variants of cuben using the thicker 0.18 mylar (ie. 1.26oz CT3.5K.18 and 1.51oz CT5K.18) will have an extremely high HH based on my anecdotal experiences. I have cuben rain pants made from 1.26oz cuben and I can kneel on water all day without getting my knees wet.

[David Olsen]

What is the style of cuben being used for these measurements? CT2K.08 or CT1K.08 or other?
More scrim, heavier mylar etc may make a difference as Dan points out.

Ryan and Roman use the CT2K.08 in their trek across AK and didn't report any problems.

[Konrad .]

This thread has def grabbed my attention. If these results hold true for all cuben fiber, then it looks like the lightweight bubble has bursted for us. Interestingly enough, Phil at sectionhiker.com did the TGO challenge in a cuben duomid, where he faced foul weather without any complaints. *Crossing my fingers, and nervously eyeing my stash of cuben goodies*

[Greg Mihalik]

Just curious which "scientific types" might be having back-channel discussions, if preliminary approaches are being defined, and when we might hear about them.

Anecdotal stories and conjectures are interesting, but "..the facts, ma'am, just the facts…" are what I waiting for.

Thanks.

[ziff house]

is getting way out of line, lets hear from some owners.

[ziff house]

How can you have zreo air porosity and not be waterproof , water molecules are bigger than gas molecules.

[Greg Mihalik]

A fabric's air porosity is measured at 0.5" of water pressure – 12.5mm – very low pressure compared to "waterproof" standards around 10,000mm, and low even when compare to the ~422mm "leak" pressures in some of the recent testing.

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