Cuben – The 422 mm hydrostatic head dirty little secret

It is my understanding that Cuben can not leak unless there is a total laminate failure am I correct? This topic interests me as I am eventually looking at a cuben shelter to eliminate the misting with sil and spinn shelters.

Hi Richard

I would LOVE a photo of the fabric in the HH tester, to see where the drops of water are coming through.

> it would serve well as a sail but it is a poor solution for heavy rain protection.
And the same applies to standard silnylon: it is specified for parachute and advertising blow-up use, not for rain wear and tents.

Cheers

Roger,

I am quite pleased to see you get involved in this investigation! I took micrographs before I conducted the tests and have included them in this post for your review.

I didn't take photos of the Cuben fabric when I originally ran the hydrostatic head tests. I will rerun the tests with photographic capture. I should be able to post these photographs within the next hour.

60X Top

60X Bottom

200X Top

200x Bottom

Brad,

I think you understanding needs to be revised as mine shockingly has.

I think we should go back to the good old days of canvas and silk tents.
Some leakage was acceptable and people acclimated just fine and didn't make such big fuss that people make about the new much more waterproof materials.

I have to agree, from my understanding of what cuben is, it just doesn't seem possible for water to pass through without actually causing obvious damage to the material.

I would be curious as to the cause as well?

Nice work Richard. When do you become BPL Staff?

I have cuben 'waterproof' stuff sacks. Now I am a little concerned….

When you set it up in your yard and it rained, did it get wet underneath?

Roger,

As you requested, I have attached photos of the Cuben in my hydrostatic head tester at 422 mm H2O. The initial leakage pattern seems to be different than silnylon. As you first correctly pointed out, silnylon seems to get little droplets at the intersections of the ripstop reinforcements. By contrast, Cuben leakage seems to start aligned with a reinforcing spectra thread without regard to the intersection of opposing axis threads. I also created a You Tube movie showing what happens with a sustained 562 mm H2O hydrostatic head; the URL for the movie is at the end of this post.

Jerry,

I stayed indoors where the wind wasn't blowing and it was nice and dry.(smile) Standard industry practice is do some sort of use conditioning prior to measuring hydrostatic head. I thought I was being very conservative in doing my conditioning using a conveniently timed three day period of stormy weather.

Hi Richard

UNREAL

Question: is the video 'real-time' or accelerated? If it is genuinely real-time, that rate of leakage is way beyond what I see for silnylon, even at 30 kPa. I would call it 'leaking steadily', rather than 'a few drops growing very slowly'. I would rarely take the flow rate that high when testing any fabric.

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.

Ah well, it was NOT made as a waterproof fabric for tents. It was made as an SUL spinnaker fabric. No specs, no promises.

Most illuminating though – thanks very much. A radical rethink may be required by some vendors!

Cheers

Neat video.

Do you think the spectra cause damage to the Mylar ?

Actually, with the sail company now separate and Cubic Tech an independent company, I think that the outdoor industry is one of their main target markets, I would think it is designed (though admittedly not originally) to be waterproof.

Richard,

I would like to see a test of the HH of cuben with the double thickness mylar. I have a good bit of the CT1K.18 that I could send you, how much do you need to get a good sampling?

Roger,

The first video I posted was in real time but in low resolution and 15 fps; the uploaded file size was 7.863 MB. I have now replaced it with another real-time video using a higher resolution plus 30 fps; the uploaded file size was 46.193 MB. Hopefully the higher resolution video may assist in problem analysis.

I was extremely conservative in the hydrostatic pressure applied. It was leaking so badly at 5.5 kPa (562mm H2O) that I never increased the pressure above this amount. Three random test areas yielded the same general results.

I will send Ron Bell and Cubic Tech an email to see if either company can offer any insights. Ron has a hydrostatic head tester; so, it should be easy for him to determine if I was sold defective fabric or if all Cuben exhibits the same poor performance.

Richard,
Was afraid something like this might happen when you got that tester. This certainly puts a whole new light on things.
Your results with sil were showing a dramatic decrease from its usual (US-made) 1200-1500mm to around 500mm HH after some use; so the figure of 422mm for Cuben is not so surprising – but the flow rate after penetration is unreal, as Roger states.

Roger,
A sample of CT2E.08 (.76 osy) will go out tomorrow. Am glad I did not give up on silnylon, as there may be more of it in my future.

Ben,
Agree. It would be interesting to know the HH of the 1.26 oz. Cuben used by Zpacks for floors, as it has a much more durable thickness of PET.

Richard,

Thanks for posting your results and video documentation.

I've been looking at new bug bivy's and shelters. To keep my pack as light as possible, I've only been considering shelters made with cuben fiber. My question for you (and anyone else who may be able to offer insight) is whether this leaking under pressure will be similar for pressure applied to the floor by the weight of a person, pad and sleeping bag?

I will be spending a lot of time on the wet, west coast of Vancouver Island this summer, and it would be a real bummer to wake up in a big puddle.

Same question as to Tyvek since it is so widely used as a groundsheet and as Roger put it "not designed for this purpose".Same question after repeated washings since so many object to "noise" For Cuben drybags it would seem unfair to assume very much hydraulic pressure since I assume they can float under most circumstances? But then again there are reviews of certain Sil-nylon /eVent drybags getting immersed under waterfalls at REI. I'm beginning to think that this type of testing is the way to separate incidental knowledge from observed standardized testing at least of batches?

Can anyone give a general description of "ISO 811:1981 – Textile fabrics — Determination of resistance to water penetration — Hydrostatic pressure test"? Doesn't it include standards for rate of rise in pressure, graduation of test pressure, time at each pressure and rate/amount of seepage? To buy the standard from ISO is about $50.

Thanks,
Lance

I referred someone who is in the business with Cuben Tech fiber and got back this comment: "I'd like to pass it on to my contacts at Cubic Tech and see what they have to say. They do make many different varieties and weight of materials some that are a TPU versus Mylar laminate. All of us who have worked with it and used it know that it changes over time kinda like crinkling up a piece of paper over and over again and it maintains strength though all of this because of the dyneema but I'm sure the mylar gets compromised over time." I can't divulge the contact's name and this tiny quote does not give away who the contact is.

It will be interesting to see which variants of Cuben Tech work out best for tarps. This is an evolving industry. Suffice it to say, this is not a final blow for Cuben Tech fiber. This contact went on to give similar stories and how fabric using silnylon has evolved over time.

So what about SPin is it the only true waterproof fabric?I want to buy a new tarp and debating cost vs lightweight vs waterproof.

prioritys would be

waterproofness
cost
lightweight.

I have owned two Spinn Shelters both from Gossamer Gear. The first one did not mist, but my newest one does mist some. It isn't as bad as some of my Sil shelters but it does mist in a hard heavy rain.

So is there no true lightweight waterproof tarps?

I was out in a record 7" of rain in mine and it was waterproof enough. It isn't bad enough to make me go back to a heavier shelter. I was going to go cuben on my next shelter, even to the point of having something custom made, but now I don't know. I look forward to more information on this topic.

There are true lightweight waterproof tarps… At least, lightweight tarps that don't mist as bad as spinnaker or silnylon. The PU-coated silnylon that Golite seems to be more waterproof than spin or sil. It's going to be a little heavier, but like the old saying goes:

light
waterproof
durable

pick two.

For light, waterproof and not so durable you could use polycro or a some other light plastic sheet.