Cuben – The 422 mm hydrostatic head dirty little secret

Ziff,

Thank you for the recent hydrostatic test you conducted and reported on. The more data points we have, the clearer the picture will become.

A lot of us lightened things up recently and had a few well needed laughs; I assume you are still maintaining that light hearted spirit. For anyone who didn’t get your (DRY humor joke) and really believes that a hydrostatic head measurement for a tarp is meant to tell you how deep the water is on top of it before it leaks, there is still hope in one (DRY writing) paragraph.

The KISS explanation is that when a thunderstorm's 4.5 mm rain drop hits your tightly stretched Cuben tarp straight it has kinetic energy just before the impact. After the raindrop SPLATS at a right angle and there is no give to your tarp it generates 10,066 mm H2O of force. If your tarp gives and moves down x times the distance of the raindrop diameter to dissipate it, then the force is 10,066/x.

The hydrostatic head measurement is tested for and published with the specs for a tent fly by most manufactures. They do this so an informed consumer can compare products to see how they might handle the force of that typical 4.5 mm diameter rain drop after it hits. It is not to tell a consumer how thick the water is on the top their tent before it leaks (smile).

Hopefully someone can test heavier 1.26 or 1.51oz cuben soon.

I wouldn't mind mailing off a sample or two of 1.25oz, but I'm not really stoked about running a few small scraps through my washing machine all day (8x) to see how they perform afterwards. If you want to test how cuben performs after wear, why not just collect a bunch of new sample pieces and then 'age' half of them all together, so one washing machine runs 8x instead of having a bunch of individuals all run their washing machines 8x?

"I'm not really stoked about running a few small scraps through my washing machine all day"

Clip them in front of a fan for 90 minutes.

Or e-mail Roger. He may be "fanning" a bunch of samples to assure consistency and would prefer the vigin fabric.

Hi all

Details at this stage are either vague or very vague. But this thread has prompted us (Richard and me) to look at doing a proper in-depth study of a wide range of fabrics to compare their hydrostatic head ratings both when new and as they age. We already have a fair bit of background data on new fabrics, but not on 'used' fabrics.

This will take considerable time to get going and to do the testing work. I for one am probably overloaded right now. But it will happen.

Now, here is an open invitation to anyone in the trade, both vendors of fabrics and vendors of gear, who might be interested in being involved. Would you like to have YOUR fabrics tested as part of this trial? Do you have the time to participate in a round trial of many fabrics? A domestic washing and a HH tester are required. Note: the testing phase will be done 'blind' (as far as possible). If two vendors are involved, they will not know where each bit of fabric came from. They will be routed through me.

Contact me via roger@backpackinglight.com for private discussions. Please do NOT use our 'private mail' system – it can't cope!

Cheers
Roger Caffin

Roger,
One wash or eight?
Or 90 minutes fluttering in front of a fan?

Thanks.

You guys do realize that the aging and degradation tests have to be done with the same piece or batch of fabric. You knew that of course. This means there can be a considerable amount of time involved. I also think that some of the preparation of fabrics for testing that we hear about can actually be far more extreme than the actual handling fabrics recieve in the outdoors. Most people's gear is going to suffer a kind of chemical degradation over time from just sitting in the gear room rather than from handling.

Richard, instead of telling us what the max impact figures are for your raindrop, why don't you give us figures for say hitting a 30 degree slope. Most raindrops are not near maximum size and don't hit pitched tarps at 90 degrees. There could easily be an inversely proportional situation here. Also, most of us, as has been stated by a few, have backup systems and layer for heavier rain like we do for the cold. I would not go out without a light poncho backup for my light rain parka, any more than I would go out with a tarp and non-W/B down bag and tarp. I would for sure have a bivi bag as well. To me it seems like you are actually arguing against the principle of going light and expect one piece of gear to do everything – ie, each piece of gear would have to be up to some kind of made up standard. Anyone who has done this stuff for awhile and knows things degrade, can be defective, and short of having brand new gear all the time, it's good to have backups and layers anyway.

By all means though let's test – testing is fun and we learn from it of course.

I have always thought a Suter Tester was the wrong tool to measure the psi of a rain drop. Hydrostatic head is the pressure rise caused by gravity acting on a column of water that is NOT in motion… Measuring static pressure is not the same as measuring the force of a rain drop…

Case in point. Cuben fiber testing out at 422mm (0.59psi).. It is by far more rain resistant then 1,000mm (1.40psi) silnylon. I have been using my CT2K.08 cuben fiber tarp for two years now and it has never misted, even in 60mph rain soaked winds. I think its time to put the calculator away and design and tool that can actually measure rain resistance.

Just remember, theoretical physics can prove that it's possible for an elephant to hang off the side of a cliff by a dandelion. Is it possible?? Maybe but the chances are slim to none and slim just left town..

"Cuben fiber testing out at 422mm (0.59psi).. It is by far more rain resistant then 1,000mm (1.40psi) silnylon. "

?

How could you even prove this? You are suggesting that Silnylon is more waterproof but not less rain resistant.

I am assuming you sell Cuben products?

Dan and any one else with a shelter fabric they would like tested,

You are correct; my plan A proposal was both inefficient of energy and it also prevented an additional hydrostatic head (HH) test after each aging cycle. The individual cycles will allow us to graph the aging cycle for each material type. Roger has been in correspondence with me relative to creating a joint test protocol that should produce identical results or at the least statistically equivalent results regardless if they are conducted partially or totally in San Carlos, CA, Australia, or someplace else. Many of the ideas below are the results of our recent collaborative discussions. It is a potentially monumental task to test, age condition, weigh, and retest every different type of fabric submission 9 times for every fabric type and source supplier that this community is interested in. Furthermore for the most usefulness after aging, the summary report should include a best fit regression analyses for each fabrics aging cycle. Hopefully the fabric’s regression should allow you to more accurately do shelter material life cycle cost analysis or estimate when your shelter should be refurbished. Furthermore the test collaboration project at some future point may attempt to quantify the effectiveness of a wide range of DIY refurbishment options through the same aging tests done on virgin fabrics. We are discussing options to try and split the load in a way that either of us can provide near real time HH initial test results after receiving a sample and then later providing an aging report. Here is the plan B proposal.

1. Forum email me to let me know you are interested in a scrap submission for testing. I will then provide you my personal contact information. Those of you that are closer to Australia or would rather have Roger do your tests contact Roger.
2. Please email the personal email address acquired in step 1) with a detailed description of the material you want tested (Purchase source, material type, source description of material, source specified oz/yd2, actual oz/yd2, and any free form comment you would like to be included in the report.) A personal email will allow us to capture the information to paste into the test report.
3. Include ideally two 1’ square virgin scraps, (one of each sample type will later be incrementally aged together using the Regular wash cycle of a Maytag A512 washer or another washer's equivalent cycle settings. If you can’t provide this standard test size, then provide two scraps, each of which is at least 6” wide on its narrowest axis. If you only have one scrap, the initial hydrostatic head test will be conducted in San Carlos, but I can’t do an aging cycle and still send an un-aged sample to Roger for archiving.
4. I will test any sample of UL shelter material
5. I will normally provide a one day turn around via a post to this forum thread with the initial HH test results
6. After we have samples of everything the forum members want tested, we will begin to focus on aging tests.
7. Self-test reports are also strongly solicited. Thanks to Ziff for being the first self-test contributor. Not everyone interpreted his test results the same way (smile) but it was valuable for everyone to see.
8. After condition testing I will forward both the virgin sample and the aged sample to Roger in Australia, via the BPL office in Bozeman. He will be the eventual repository for every sample submitted to either location and he will be the arbitrator for any anomaly noted by a forum member.

To be fair to Ziff I did kind of put words in his mouth – not sure he liked the taste yet. We all look forward to the rules you come up with so we may break them in due haste. (smile) I think you should require at least one photograph of the testing device for self-testers – to eliminate as many interlopers as possible, and I think all aging should be done in Oak Barrels.

In the interests of full disclosure Richard…..it sounds like you are working for BPL. Did BPL fund the HH tester? I remember you saying something about the head being aluminum – what's the brand and model?

you read me correctly, [smiley thing].
Richard ,all in good fun, no sense getting wet over it.

Dan,

I was just attempting to follow KISS. The calculations for the force on a small spot are extremely complicated when you factor in all of the variables. For example you are correct that the angle is one of the variables, 30 degrees is a more realistic tarp angle, and this will reduce the force. Offsetting this factor, Cuben doesn't give like silnylon does and so the pitch angle and the give almost offset each other.

I think depending on the locations you will be backpacking in (general indicator of the typical rain drop size) 1,200mm on the low end and 3,000mm on the high end are realistic HH targets after you either do all of the complicated calculations. The EU has a full set of regulations to protect consumers. The EN 13537 standard for sleeping bags is an example. The legal definition for the minimum HH to advertise anything as waterproof is another. Their law is also a reasonable lower limit for the US. We have more variable weather conditions. REI sets the bar at 3,000mm to maintain profitability with you can return anything at any time if it doesn’t perform as advertised is what I personally define as the limit of what you need.

My current trust-my-life-in-extended-bad-weather tarp is a MLD Duomid that I boosted up to 1,400mm for only a 2 oz penalty by recoating the silnylon with mineral spirits and Silicone. That brought it back to better than new status. I am a fanatical gram counter and if I can find comparable coverage and HH for less weight I will switch.

We all have different hierarchies of importance. For some people it is the lightest weight without a minimum threshold for HH. My personal hierarchy is the lightest weight, a minimum HH as defined above, and acceptable life for a multi-month trip( I am commonly in the bush for 1-2 months at a time).

I know enough at this point to know that I don’t know what the answer is to the question, "Which material offers the best combination of lightness, toughness, and HH." Hopefully some additional testing may answer my question.

I don't buy that the 30 Degrees of tarp pitch is offset by the taughtness of the pitch of Cuben. The give of the sil in a local sense can work against it and diminish the advantage of the pitch, whereas the taughtness of the Cuben pitch maintains the advantage of pitch.

The flexing absorption of energy the sil can do by 'cratering' in the local of a raindrop could balance out with the Cubens lack of cratering. In may require more HH for the sil to overcome it's flex and pocketing of a rain drops force, than a Cuben sheet that lets it go on down the tarp without resistance. In other words, the Cuben is better at martial arts and gets the drop rolling down the tarp faster.

I'm no scientist, but it seems that beyond measuring HH on fabrics, how about looking at them under a microscope as well? It would be interesting to look at a virgin piece of fabric, then HH test it, then look at it again. This would give some kind of understanding if the machine plays any part in these low HH numbers. Maybe the microscope test will not be able to "see" a large enough surface area to make reasonably statistical conclusions, but you understand what I'm getting at. And if this can be carried out across virgin and aged samples, it may provide another meaningful data point. But, that still leaves the hard part, correctly interpreting the data. If the findings don't adequately explain field experience, they may not be reliable either. And that's what I beleive everyone wants and the reason for this thread and its rather heated discussion. Heck, it is the current post leader in front ot the "Friendly expertise on camping" thread. -Richard, Dan M., Roger, thanks for the interest and effort in getting to the bottom of this. It will be helpful to the industry, I'm sure of that.

That's a good idea. It's possible it won't even show up there but that's a good idea. This is my current microscope by the way – an R8900;

http://cgi.ebay.com/1964-BAUSCH-LOMB-MICROSCOPE-SET-Original-Box-/220754606777

I bought it at a thrift shop for $2.95 without the goodies listed above. They don't make toys like they used to – I can say that. That little guy has amazing clarity. It's the real deal. Business has been pretty good so I'm currently shopping for an upgrade. I would like to get a stereoscope.

I think that by using dyes along with microscopes, we may be able to track where the water went and leaves dye. Where it went may show an unusual path – mainly the Cuben would be unusual in this respect. Even real time it may be possible to watch the path. It's possible that a tiny section in the mylar can be breached somewhere even in clamping the fabric and then the water could flow somewhere else and breach the mylar in the opposite side.

It could probably only act like this under continuous and unrealistic pressure of course. Hey Warren, if you're not a scientist, what……You don't think I'm a scientist do you? Haha! (smile) My first job when I moved to Washington when I was 13 was tapping water mains in a housing project. My Dad had the real job but I used the money to buy my first down bag at Eddie Bauer, and a Primus stove. But getting back to the relevance, I guess my plumbing instincts could help out here.

Hey David,

I have said it before and I will say it again..Hydrostatic head measures the psi of a column of STATIC water, NOT the psi of moving water or in this case a rain drop.

The only proof I have is that in 60mph rain soaked winds my CT2K.08 tarp wasn't misting. I really don't feel like breaking out a calculator to figure out some hypothetical hydrostatic head number but I would assume the rain drops were around 3mm and they were hitting my tarp around 60mph which should be somewhere around 10,000mm. I can say for sure that my silnylon tarp tests out at 1,000mm and in these same conditions it would have been misting.

Find one person that has said their cuben fiber tarp/tent has misted..I bet you wont find one. Do the same with silnylon and the list is endless.

As you mentioned, I sell cuben fiber products. For its weight, strength, tear and water resistance no other material compares.. Do I think it has downfalls? Sure.. All materials do. But its down falls to me are its low abrasion resistance and the fact that sewing weakens the material..

Lawson,

There is a GOOD correlated INDICATION of (dynamic) rainfall resistance from the (static) Suter test hydrostatic head reading. That is why it is standard practice for all large tent manufacturers to Suter test their rain flies and include this value in their tent description.

Source: Clothing test methods By National Research Council (U.S.). Subcommittee on Clothing, Louis Harry Newburgh

"… of the simple routine tests, the hydrostatic pressure tests, group(3) are perhaps the most informative, since they measure a quantity which is influenced by both fabric construction and finish. Within any group of comparable fabrics, the hydrostatic pressure test provides a GOOD INDICATION of rainfall resistance…"

Now, I'm completely out of my league here with this science stuff, but wouldn't it be cool (and useful) to have a device that is capable of firing a specified size water droplet at a specified velocity? Couldn't be too hard to make….. I mean, we put a man on the moon in the '60's!

They still make garden hoses don't they?

Richard, you pointed out that Cuben and Sil act differently when pitched yet the HH test really does not take that into account…….but, they main thing that comes to mind in thinking about this is that we don't seem to have an equivalent weight of any fabric to the sub 1 oz fabrics to even test against the Cubens, Cubens that go on down to the half ounce range. If there is no fabric even in the same realm of strength and water resistence how do we really compare them? In considering it's ability to pitch tautly, and how this probably adds to it's water resistence that does not show up in the HH test, maybe we need to be judging it with a weight/strength/water resistance quotient, instead of trying to demean it with standardized testing? You call it Cubens dirty little secret. That's a pretty good secret if you ask me, that Cuben is in a realm of it's own that NOTHING else can touch. You have yet to compare an equivalent weight of Cuben and Sil, yet you think it's relevant to maintain the title of this thread. I find it interesting that you typed it in the first place. You mean to tell us you have not been able to get your hands on some weight of Cuben to do a fair test on something closer to Sil? Maybe you just like headlines. If nothing else it's good for Cuben.

Guys, to get a vibe for what a fabric is capable of regarding wind driven rain, you need to measure its impact resistance and its porosity. Its not JUST its HH. Its a combo of both to get "misting" through said fabric.

Of course you still have the weeping problem due to capillary action. This is directly proportional to HH. IE soft continuous rain.

A fabrics hydrostatic/hydrophobic properties are what will also determine how much condensation will form on its surface before forming a drop and rolling down the inside face of the fabric to the ground or if in a "bathtub" style tent, onto the floor.

Its not just HH.

Wind driven rain with condensation on the inside of a tent never happens in my experience. Most common issue is condensation, not 'misting'. This happens when the air is generally calm thus the wind won't be flapping the tent all around blowing said condensation onto your sleeping bags. Thus, materials with super high hydrophobic properties will roll drops of water on them faster and have said drops slide down the inside face of the tent/tarp and onto the ground. I find this property to generally be a better measurement of how well it will perform for keeping you dry. That way if you do rub up against said fabric, it will be dry, erm "DRIER" anyways.

Cheers

Dan,

My HH tester was purchased by me for my personal use. It was custom designed and built by a large fabric manufacture for use in its distribution network. One of the distributers dropped the line and I purchased the unit from them.

I am not part of the BPL staff and have never received even $.01 from them. I am just a forum contributor. If you go back in the archives and look at my early posts relative to whether down loft was an accurate determinate of its insulation value, some of the staff was as rough on me as you have been (smile).

I think your idea of requesting a picture of the test device is a good one. Ziff's cardboard tube should probably be excepted. Your aging idea is also a GREAT one… samples please?

Warren,

I agree that micrographs are another valuable tool in our arsenal. You will see a set in the fourth post of this thread.

Damaging fabric is prevented by testing light shelter fabrics per 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 until you see 3 droplets. The pressure rise is stopped as soon as this occurs.

Hi Dan

> we don't seem to have an equivalent weight of any fabric to the sub 1 oz fabrics to even
> test against the Cubens
Very true.

> maybe we need to be judging it with a weight/strength/water resistance quotient, instead
> of trying to demean it with standardized testing?
Don't think so. I would be more interested in whether I get wet – whether it leaks.

If you are walking in the dry season and not expecting anything more than a light shower or two – there's probably nothing wrong with a UL Cuben tarp, plus a bit of skill pitching it. It's all about picking the right gear for the conditions.

Cheers

Thank you Richard for this generous offer of your time, my samples are already in the post. I appreciate this and believe that the final results will be a valuable resource for all on this forum.
Only when we have these results can we then have the debate as to whether they correlate with experience and if not then why not.

In the meantime it would be more constructive if those with criticisms or complicated alternative suggestions would contribute more than just words, which take no effort at all.

When my wife read this stuff she said a hydrologist would use a dye test to determine the
difference between condensation and penetration by rain. Dan mentioned this. It is what
a water scientist would do. Come at it from a different angle than a fabric scientist.

Point of interest- I have one customer who camps in the sub zero and does not want
"waterproof" tent fabric since he doesn't deal with rain. He likes double layered
DWR pyramids.

This makes me think of Black Diamond's Epic tents. Wonder what the HH is for this?
And how about the steep sides of a teepee made of Epic. I think Ti-goat makes these.
Does this make enough difference for the shelter to be rain worthy?

As for a column of water on top of a tarp, I have seen plenty of new tarp-ers set up
shelters that would make a bathtub proud.