Cuben – The 422 mm hydrostatic head dirty little secret

"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."

Ah, the sweet voice of reason.

FWIW, here is a bit of anecdotal evidence from an online reviewer:
“I can say for sure that the [Cuben-fiber Rocket Tent] is dry. The fabric is waterproof. It rained, and occasionally snowed big, wet flakes, for about twelve hours straight. Every piece of fabric that I had with me got wet. The outer layers of all my three-layer, waterproof fabrics got soaked; the pack was soaked; boots; gloves; you name it. And I wasn’t ever out for long. The tent didn’t let one drop of water in. As a matter of fact, when it was time to take it down, I removed all the anchors and ski poles, and just held it by the probe in the wind. It flapped away for about three minutes, and was pretty much dry.”

Roger said he did not 'think' Richard said Cuben should not be used for a shelter either. Here's what Richard said after saying it's a POOR SOLUTION for rain;

"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."

At Risk? Sweet voice of reason?

"At Risk? Sweet voice of reason?"

Dan – I was referring to Roger's last post. Maybe I should have qualified it by referring to Roman Dial's earlier comments about a Cuben shelter being his go to for many of his hikes in Alaska, known for its wet weather. He did say that for worst conditions, he used silnylon, though, IIRC. It wasn't a matter of total waterproofness for him, rather enough waterproofness to justify its lightness and protect him from the worst of the downpour. Tradeoffs you make in the real world?

Sorry Tom, I was just pointing out the quote you selected was largely untrue regarding what Roger said Richard said.

Roger said this about Richard; "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 then supplied what Richard said early in the thread. You must have missed it. It's very easy to deduce that Richard does not think Cuben should be used for shelter. It's as good as saying it.

Two weeks ago I posted the HH values that I personally define as waterproof and a brief explanation as to how I calculated them. For what it is worth, they are similar to what the above sources also define as waterproof. See: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=43902&skip_to_post=373814

when you guys get all done being sciency, will someone please PM me and tell me to whether or not to trade in my spinntex tarp for cuben?
thanks,
a layperson

Roger, I wanted to point out that I believe you are assuming Spectra is a hard thread when you say this a few posts back;

"In other places the total thickness will be that of two layers of Mylar film PLUS two layers of very hard Spectra thread."

Because you say that, I don't believe you are familiar with Spectra. It is a strange fiber and is very supple and can morf quite readily around corners. If the Mylar gets compromised, it is in the HH machine doing the testing. That's not cool. I said something similar but only in reference to the mylar being damaged during testing, not during manufacturing. Cuben does not claim to use Spectra anyway, but the dyneema is similar.

It would be interesting indeed if it was the machine causing the relatively low HH numbers because it damages the fabric. I'm not going to count on that though.

My cuben tarp has never leaked. But then I do not live in the PNW. But it has been is some serious thunder storms. I can also tell you that a mouse can chew through a cuben sack.

Last night I had dinner outside of my tent. Temps below freezing, my Fugu jacket kept my body warm (thanks Richard), and the pack pad from my McHale kept my butt warm and dry while sitting on snow (thanks Dan), these are the things I look for; functionality.

is da' bomb man..

I see Event is listed at 15-30000mm, there's another big debate, how come i always get soaked when i wear that thing?

=>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.

I'm not sure how you got this number. It seems to me that 422 mm is less than 1.5 feet of static water. Of course, static water on your tent/tarp is likely to be less than a few mm deep (unless it is pooling). If the water were wind-driven or falling (as rain tends to do), then I imagine you would need more than a few mm of HH resistance in your fabric to stay dry.

I am not sure; do we have a number that is the accepted number for HH in a tent or tarp? Is 1000 mm just some arbitrary round number that is close enough to waterproof or is it what we should be looking for in a tent fabric?

Wayne

Jeff,

Equilibrium allows a somewhat porous 10 CFM and typically doesn't have a good DWR treatment; so it is not the ideal for the Fur-tech concept but it will work. Fix the DWR by washing the jacket in non-detergent soap, add a good fluorocarbon DWR like Grangers, and dry at 140F for about 15 minutes to set the DWR. Add a thick fleece under it and it should act like a regular WPB rain jacket ensemble.

Wayne,

I am not sure if your question is addressed to a specific person. If it is an open question, then my answer is 3,000 mm if you want to avoid misting from low HH. 1,500 mm is Ok if you have a bivy or WPB shell on your bag to shield yourself from mist related to low HH. This answer assumes you will be camping in areas that are vulnerable to Thunderstorms with typical 4.5mm max drops.

1,500 mm is the minimum European HH standard. 1,000 is a fur-tech proposal based on wearing a thick fleece under a 1,0000mm garment.

Richard, couldn't somebody just take a clear tube and hose clamp some fabric to the bottom of it to create a tester? All you have to do is graduate the cylinder and make sure the clamp or clamps don't leak. Am I correct?

Now I know why I should not have skipped science class to go out and run when in school. :(

Hi Dan

> I don't believe you know much about Spectra. It is a strange fiber and is very supple and
> can morf quite readily around corners.
As I mentioned before, I spent 27 years in textile research, ending up as a Senior Principal Research Scientist with a large research group under me. I do have some knowledge of fibres and textiles.

That you can bend Spectra or Dyneema around a corner has more to do with the diameter of the fibres than their hardness. I can bend selected glass fibre fabric around sharp corners too, and we all know how hard glass is.

Cheers

@Richard: I would love to see the same tests done for the common WP
B materials used for shells. I would particularly like to see the changes in HH rating in 4 situations: new material with fresh DWR; new material without DWR; used ("conditioned") material with DWR; and used material without DWR. I strongly suspect from my own experience that the common WPB fabrics (Gore-Tex for example) will be effectively waterproof with and without fresh DWR, but after use, the DWR will make a huge difference to the waterproof rating. I really hope you are able to do these tests because they will provide the first openly available data points about the true waterproofness (or not) of the common WPB fabrics.

@everybody :)
Putting aside arguments about whether or not test results such as these are directly applicable to the real world, I'd like to thank Richard for this and ever other post he has made on BPL. They are all bookmarked and referred to regularly by me, and I suspect, many others.

For me, the importance of this particular thread is in two points. The first is that there is a lot of variation in the waterproofness of material might think of as interchangeable (ie. not all silnylons are the same!). The second is that the waterproofness can change drastically with use and age of the fabric. This is a really important point I had not considered before. For me it means I need to think about looking after my shelters the way I look after my rain gear.

> 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.

Unfortunately many would have to disagree with you. We have good reason to believe, from both theoretical modelling and from actual experiments, that large raindrops driven by a strong wind can easily exceed that pressure on impact on a stiff surface. Now the middle of a large span of fabric is not stiff, but there are places on any tarp or tent where the surface can be said to be 'stiff'. Water can leak through there.

> I don't understand your resistance to seeing different meanings of what waterproof can be
I would like to think that when something is called '100% waterproof' that it won't leak under quite low pressures. Ymmv.

cheers

> 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.

Hum – I do have the published research that figure of 5 came from. It was based on fairly extensive experimental research.

Cheers

> Roger said he did not 'think' Richard said Cuben should not be used for a shelter either.
> Here's what Richard said after saying it's a POOR SOLUTION for rain;
> "Unless …. I will probably never buy another Cuben product.

We tend to be fairly careful in how we use words. Saying I will probably never buy is a statement of personal opinion or decision. Saying Cuben should not be used for a shelter is a recommendation to others. In my eyes they are totally different.

Cheers

Dan

> It's very easy to deduce that Richard does not think Cuben should be used for shelter.
> It's as good as saying it.

Here is where you and I disagree. You are extrapolating from what Richard wrote; I do not accept that your extrapolation is valid. I think Richard uses words far more carefully than that.

cheers

Dan, yes. You could certainly do that. Some materials will respond differently to small diameters. Example: aluminum foil. You end up testing the weight of a volume of water, which can change with diameter, not the permeability of the membrane. The small diameter can become important due to capillary attraction which can influence small tubes. This is the same basic principals as a water level, though…just raised at one end. Also, contact with a surface can change the permeability at the edges, as can stretching(especially with laminates.) The
clamping scheme you present is likely too variable to give good results. Preparing small samples will be a hit or miss proposition with a likely large variability in results. A 40-200x microscope with lighting should enable you to see if a sample is properly mounted and if a leak occurs at the edge. I believe someone sugested a 4" tube. But I am not sure how he went about reading it. A seperate set of fittings and clear tube would have been needed. A messy job, that. How do you drain it inbetween tests?

But, overall, that is the basic concept. A tube with a sample clamped to the low end.

"I see Event is listed at 15-30000mm, there's another big debate, how come i always get soaked when i wear that thing?"

Because you are sweating like a one-legged man at an arrse kicking contest. Try one with pit zips or slow down….or wash it to improve the breathability.

idiot wrote this ''unless under sreious pressure [sittingfor extended periods,heavy peolpe sitting] ''
The HH for a submerged surface would be equal to the weight of displaced water, in the case of sitting on a wet surface or small pool this would be grams ,micrograms?
Perhaps they the real concern there would be abrasion of the material, which is why we use ground sheets.
DON'T WALK ON YOUR CUBEN [on a hard surface] , it will leak for sure.

i'm convinced the the water vapor permiability runs both ways, and at the same time you cannot squeeze water though that stuff. For example, i will be wearing multiple layers ,the inner ones are wet with sweat but the ones next to the event seem heavy with water. I think its one of the oddest materials i've seen. By comparison my Propore jacket breaths really well and while my clothing may none the less get damp from sweat its not really wet as with Event.