I recently purchased a commercial low pressure hydrostatic head (HH) tester (0 – 3,515mm H20). It is neither low-cost nor portable; it weighs over 23 lbs. even though the bulk of the system is aluminum and it is quite bulky. The pressure system consists of an electric water pump and control valves; consequently HH tests can be completed quite quickly and accurately. The test head is approximately circular with a diameter of ~4.5”. At the upper end of this systems test range, the fabric looks like it is going to explode. Consider that this level of hydrostatic head is a water column that is 12’ high and you can understand why. There are HH units that will test higher pressure than this but fabric damage (sometimes catastrophic) is not uncommon above a 12’ water column.

Waterproofness
Water-pressure measurements are shown in millimeters (mm) or pounds per square inch (psi); 704mm = 1 psi. This is the height of water column in which water starts to pass through and bead up on the other side.

Water resistance in fabric is determined by employing a water column or hydrostatic pressure test (JIS 1092 method A; AATCC test method 127). Fabric samples have been laundered 10 times to simulate field use.

What level of water resistance qualifies as waterproof? No widely accepted waterproof industry standard for fabric exists. On the low end, REI considers rainwear fabric to achieve a minimum standard of "rainproof" performance if it permits no leakage at 3 psi (2,112mm). On the high end, the US Armed Services most frequently define waterproof as 25 PSI (17,575mm).

I am just starting to look at the question of shelter HH values. I tested four of my shelters so far: a Six Moons Designs Gatewood Cape that I have used about 10 – 20 days in the field; a new Mountain Laurel Designs Serenity Shelter; a Mountain Laurel Designs DuoMid which I have used about 30 days; a Black Diamond Megalite which I have used about 60 days; and a new Golite Shangri-La 5. The following are my test results including the fabric thickness in mm, a 200x microscope photo of the test area prior to the test, and the hydrostatic head of the test area. If others have recently calibrated HH testers, please add your test results to this thread including the number of field days the shelter has on it.

Six Moon Designs Gatewood Cape (After 15 days use)


200x microscope picture
Avg Fabric Thickness .08mm
Hydrostatic Head 211 mm H2O

Mountain Laurel Designs Serenity Shelter (Unused 2011 version)

200x microscope picture


Hydrostatic Head Tester showing this item at 1,195 mm H20 (note that most of the droplets start at the intersection of the rip-stop grids as Roger Caffin has previously discussed)

Avg Fabric Thickness .08mm
Hydrostatic Head 1,195 mm H2O

Mountain Laurel Designs DuoMid (After 30 days use)


200x microscope picture
Avg Fabric Thickness .08mm
Hydrostatic Head 562 mm H2O

The above DuoMid was tested a second time after being coated with a 1 part silicone to 3 part mineral spirits. It was brushed on multiple times while still wet from the prior coats in an attempt to maximize the coating amount. It was tested after the coating had dried but it has not been used in the field.


200x microscope picture
Avg Fabric Thickness .10mm (resulted in a ~ 10% shelter weight increase)
Hydrostatic Head 1,406 mm H2O

Black Diamond Mega Light (After 60 days use)


200x microscope picture
Avg Fabric Thickness .08mm
Hydrostatic Head 562 mm H2O

GoLite Shangri-la 5 (2011 version unused)


200x microscope picture
Avg Fabric Thickness .05mm
Hydrostatic Head >3,515 mm H2O

Edited by richard295 on 03/05/2011 22:41:03 MST.

Interesting results. The advantages of being able to spec and purchase in volume?

> GoLite Shangri-la 5
> Hydrostatic Head > 3,515 mm

The obvious point here is this shelter is new. The HH will be reduced as the fabric is abraded with use.

Those are very interesting, especially since I own one of each, except the Gatewood. (Actually my Golite is a ShangriLa 6, but I'm hoping it's the same fabric)

Could you let us know how old your Duomid is, and whether or not it uses the post 2009(?) Shield fabric? I have to admit I was kind of expecting the Duomid to do better than the Megalite.

Rod

Interesting, impressive results from Golite. But have you experienced any leakage with the other shelters in field conditions?

If people are using shelters with a HH head of ~500mm in storms and experiencing few problems then it appears that HH is not terribly important...

Edited by jamougha on 03/05/2011 06:29:14 MST.

Thanks Richard. I love your posts. I don't understand why you are not on staff here at BPL. I recently bought an emergency shelter for winter day trips with my kids made by brooks range:

http://brooks-range.com/alpini-shelter400.html

It is made out of uncoated ripstop nylon that has been "calendered" to be waterproof. It is very light, compressible, has an interesting tacky quality to it. Since it is not coated, they say it won't lose its effectiveness and gets softer over time. They claim it is waterproof to 1 PSI, which puts well within the range of what you are seeing for coated, nonbreathable silnylon. Do you have any experience with calendered nylon? If it is truly waterproof and breathable in a light thin single layer it seems very impressive.

For my purposes in the winter, actual waterproofness is not that important. The material may be "breathable" but there is definitely condensation and a dramatic rise in humidity inside, but then we are pulling it over our heads and breathing inside.

thanks.

Hi Richard. Thanks for again sharing some interesting info. with us. I'm curious if the results you posted were the average, mean, etc... of multiple tests per shelter, and if so - how consistent were the results?

Very interesting Richard, thanks for getting that and posting results

I wonder if silnylon that has a "misting" problem corresponds with a lower hydrostatic head

Another thing I've noticed is that if I put something on the dry side, it will sometimes wick water through, like for stuff inside a pack. I wonder if some hydrostatic head theshold corresponds to this.

I wonder how hydrostatic head varies with time. Is a fabric waterproof when you buy it but does it start leaking after you use it for a couple years?

Yet another fine and useful Nisley post! Thanks Richard. I was quite disappointed to learn that you'd been at the recent Bay Area BPL shindig but I missed you due my very late arrival.

One comment about the post manufacture treatment ... in addition to the 3:1 dilution factor I think it'd be useful to report the weight/yd^2 of the additional silicone applied.

Once again, thanks for all the info you share here.

Thanks Richard. "Truth in Advertising" (of products) is found by scientific testing.

If you ever get the chance please test one of Eddie Bauer's First Ascent WP/Breathable parkas. I expect their claims are correct but an indeopendent test would be nice to have.

EXECUTIVE SUMMARY – You want the highest possible HH to begin with because silnylon degrades rapidly from handling. You can restore the HH head close to the “when new HH” by applying a coating of silicone diluted with mineral spirits. The optimal ratio was not tested for.

I updated my original post to include an unused 2011 MLD Serenity Shelter’s silnylon in my test results plus a photo of the test head at its HH limit. The 2011 MLD silnylon fabric tests 1,195 mm H2O. This test, as well as all others, was repeated three times on widely different parts of each shelter. Only the average value is given. The standard deviation for three different areas averaged only~70 mm and so the average value is most relevant.

Yes, I have experienced "leakage" in field conditions which some portray as "condensation" and some as "misting". My most vivid memory, but by no means my only silnylon leakage memory, was in my then new DuoMid which I ordered 10/12/09. About one month later, after it arrived, I took it on a coastal CA kayak trip during the peak of the winter storm season. The forecast called for heavy rain and wind resulting in the group's head count dropping from about 20 people down to 2. I thought what great weather to test out my new DuoMid. I was one of the two people who spent a week out in the very stormy weather. I was sheltered by the DuoMid with a Titanium Goat bivy inside. The bivy’s mosquito net was over my face but still the cold water hitting my face through the netting prevented me from sleeping until I strapped my wide brim Tilley hat over my face and breathed through its side ventilation.

The manufactures’ spec on average is 1,200mm H2O HH for silnylon. Jim Wood and Roger Caffin’s prior tests seem to concur with the validity of this “when new” value. The “when new” values caused me concern and my “when used” values caused me even more concern.

-The consequences of misting-
It is desirable to avoid condensation and there have been many BPL articles explaining ways to minimize this phenomenon. Basically the articles explain that it wets the surface of your clothing or sleeping bag if you rub against it. Misting and its consequences seem to be less well understood. A fine mist flash evaporates after absorbing the heat from your warm micro-climate, effectively reducing the ambient temperature. One gram of water mist evaporation gives the same cooling effect as the melting of seven grams of ice. Worst case it can cool the local air temperature significantly. Misting in a cool weather shelter is the antithesis of thermal efficiency. In simple words, “IT IS UGLY AND IT SHOULD NOT BE ALLOWED” (smile).

-Rain never causes enough pressure to cause silnylon leakage explanation-
Three pieces of information appear to be at odds with this explanation.

1) When I conduct hydrostatic head tests, micro droplets form on the side opposite the pressure. During a rain storm, it would be impossible to differentiate from a micro droplet of moisture caused by condensation versus a micro droplet of water from pressure leakage.
2) Raindrops commonly vary from about 0.6mm to 6mm. Uncommonly, the rain drops are in the 9 – 10mm range. The larger the raindrop size then the higher is its terminal velocity and its’ resultant kinetic energy. The common range of 0.6mm to 6mm raindrop kinetic energy variance is greater than a 5,000 fold difference. I will avoid the resultant force calculations because the math is quite complex because the variables are the thickness of the water film, the angle the raindrop hits, the peak versus average force, and how much the silnylon moves from the force.
3) Conventional double wall tent manufactures determined by experimentation that if the fly has a HH of at least 1,500mm, then the inner tent prevented any customer complaints.

-The HH figure provided by your shelter manufacturer is rarely tested by the user when new (they typically don’t know what HH they started with) and it will always decrease with use (they don’t know what it is currently)-

1) In all my years of reading BPL I cannot recall a shelter review in which the manufacturers’ HH claim was ever verified with calibrated equipment. In some cases, even the shelter manufacturer doesn’t do a calibrated HH test; they just specify what their fabric supplier specifies. As a result, we don’t know what HH we start with.
2) Every time you stuff your shelter in your pack and then un-stuff it from your pack, the HH will be reduced from whatever it started at.

The Belgian Army has conducted an extensive long-term study of parachute wear on systems used by the school. They were very interested in the effect of high altitude deployments possibly accelerating the performance degradation they were experiencing on their main canopies. From the first part of their study, they concluded that there was no direct relationship between the exact number and type of jumps and the degree of increase in porosity measured, though the porosity increase was great enough to affect performance. They also concluded that the handling during packing was much more detrimental to the parachute than the actual deployment and use.

This led the Belgian Army to question their beliefs about their reserve parachutes, "which we assumed would stay brand new forever." In checking some reserves in their systems, they found porosity readings as high as 18 cfm in some areas of a parachute after only 30 repacks had been performed. A full 32% had porosity readings of more than 9 cfm... The original mil specification, now a PIA specification, for the fabric used on this particular parachute requires 0-5 cfm when new.

-I am as confused as many of you-
*Although I now know the HH of my shelters now, I have no idea what they were when new.
*I don’t know the degradation curve with use for the materials used in my various shelters. Furthermore I don’t know the relative contribution of stuffing versus UV degradation.
*I don’t know what the most efficient remedial action is to add HH to a degraded shelter. Ideally the HH of a flat tarp should be measured when new and then periodically monitored until either the degradation stabilizes or reaches 50% of the new value. One foot square should be marked with a magic marker to compare remedial actions. Examples to test include: Silicone in light dilution, medium dilution, and heavy dilution; and all other possible coating products.
*How does the degradation curve of a rejuvenated fabric compare with a new fabric?
*One of the related forum posts said, “If people are using shelters with a HH head of ~500mm in storms and experiencing few problems then it appears that HH is not terribly important”. R value for pads, EN 13537 rating for sleeping bags, and HH ratings for rain shelters may not be important because people are experiencing few problems. Yes, if it is not broken, I should not waste my time trying to fix it… time to go hiking.

Edited by richard295 on 03/05/2011 14:59:31 MST.

Stuart,

Your point is valid but also consider that the new MLD Serenity Shelter silnylon only tested 1,195 mm H20 versus > 3,515 for the new Golite Shangri-La 5. I plan to conduct periodic HH tests on both the Serenity Shelter and the Shangri-la 5 after equivalent days of field use… time will tell.

Edited by richard295 on 03/05/2011 14:33:59 MST.

Michael,

I have not done any tests on calendered nylon yet. 1 PSI should be OK for snow but I wouldn't use it in the rain.

Jim,

My Duomid shelter weight inceased by 10% after putting on as heavy a silicone coating as I could. Assuming the silnylon was 1.3 oz when I started then it should be 1.43 oz/yd2 now. Sorry I missed you at Henry Coe.

Yep, silnylon kinda sucks at keeping you dry.

Richard,

Thanks for sharing your test results. I always look forward to your posts. Your practical experience, scientific expertise and easily understood explanations are much appreciated.

Hope you can get away from your testing and take a much deserved hike.

Gary

" “If people are using shelters with a HH head of ~500mm in storms and experiencing few problems then it appears that HH is not terribly important”. R value for pads, EN 13537 rating for sleeping bags, and HH ratings for rain shelters may not be important because people are experiencing few problems. Yes, if it is not broken, I should not waste my time trying to fix it… time to go hiking."

Hmm, I hope you didn't take my comment as a dismissal of your work, which is interesting and clearly valuable.

My point was that these HH numbers are so far below the accepted values you gave for waterproofing (3,500-17,000) that, if the shelters were performing adequately, then those conventional values would appear not to apply to single-skin silnylon shelters.

It's fantastic that you plan to work out some kind of degradation cycle for silnylon, but along with that we need some idea of an acceptable HH lower limit. Right now I have no idea what that might be other than 'more is better'. If it's 1,500mm+, as in your study by manufacturers of double wall tents, then an awful lot of happy MLD, SMD etc customers are failing to report significant issues, either through ignorance or other reasons.

(Maybe my next shelter will be cuben...)

Edited by jamougha on 03/05/2011 15:23:58 MST.

"an awful lot of happy MLD, SMD etc customers are failing to report significant issues"

+1

I think one of the most interesting things that could come from this is the attempt to re-waterproof the nylon. I'd like to see the effect of the light silicone mix used for seam-sealing, and some other methods, like the Atsko (spelling?) silicone spray. I could send you my new Rainbow, and you could test it, and send it back. After you seam sealed it for me!!

The HH of the silnylon I am using to make my next shelter is specified by the supplier as: "2000mm after abrasion".

This fabric is listed as 2nd quality product and the supplier also provides the additional information: "This fabric is 2nd choice because the hydrostatic head doesn't meet the requirements for expidition use (2500mm after abrasion)."

I didn't know that there is a test that specifies abrasion, or how much and how that abrasion is applied.

I also don't know what the HH of the fabric is as new...