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Marc,
You said, "This is a potentially great data and could explain a lot of different perceptions and beliefs. But I have one significant question – @Richard – What are the sources of your data?"
My post was not a copy of someone else’s work… I uniquely created it by culling relevant fabric specifications and lab tests.
Richard:
Thank you for your reply, but something else must be at work here, because 1500mm is equal to more than 59 inches, and we all know that's not how thick the coating on a tent fly is. Also, think of the marketing potential–if the fabric plus coating really proved to be that waterproof, why not advertise a 56,000mm rating? But then checking your figures for eVent, it seems that another rating system is used for clothing that might also be what North American tent manufacturers use in describing waterproofing: mm of water per 24 hours–which is something completely different from the hydrostatic head test. Confusing, no?
From my experience with a MH Trango tent floor (brand new) that would pass water from the inside to the outside under pressure of my body on a thermarest (let's say a force of 7 PSI), I believe that the rating of 3,000mm by Mountain Hardwear probably is referring to the hydrostatic head rating–7 PSI is about 48 kPa, and from what I've read, a 1,000mm hydrostatic head rating is equivalent to 9.8 kPa.
However, I did find this on the Internet, which gives a different interpretation of hydrostatic head vs. PSI:
"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.
"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."
Richard, you stated that a thunderstorm can generate a hydrostatic head of 13k mm. Can I assume this is a truly exceptional storm? What's a "typical" storm generate? Are there any tables which suggest water pressures that various conditions are likely to generate?
I know that I have seen sil-nylon mist, so I know a moderately bad storm will generate 1500mm. On the other hand, I have been in shelters with a 3500mm rating in what I though were pretty harsh storms which included rain drops that sounds like gun shots propelled by 40+ mph winds. No misting or leaks.
–mark
Mark,
All falling objects have a so-called terminal velocity, a speed they can’t surpass due to air resistance. Therefore, larger rain drops generally fall faster because their heftier size helps them power through air resistance more easily than little drops.
Droplets that reach 0.2 mm, the threshold for calling a drop rain, are usually heavy enough to overcome the force of ascending air that exists in every cloud. Rain can be either "cold rain", originating from melting snowflakes, or "warm rain", which evolves without the snowflakes. Cold rain has very large drops, but fewer drops overall. Warm rain contains very many, but small drops. Raindrops can range in size from 0.2 mm in diameter, to around 6 mm. Those larger than 6 mm are inevitably broken up in their fall to the earth. 8 mm is only common in a typhoon.
The size of the rain drop will determine its terminal velocity and its hydrostatic pressure. The temperature will also vary the terminal velocity with colder temperatures providing higher velocity; this spreadsheet is for 50F. Every resource uses different names to define rain drop sizes but the following is an overview.
The static water pressure of rainfall is calculated according to rain drop speed except for the last row (typhoon). Wind also influences the water pressure of rainfall. When subjected to wind velocity of 20m/sec (44.7mph-comparable to a typhoon), the static pressure of rainfall is estimated to reach 35,677 mm.
Setting aside the new fabric's performance in the field vis a vis precipitation resistance and breathability (tendency to form condensation)–which await emperical data through field testing–will the new tents be "legal" to sell in the many states that Epic tents are not?
Cheers,
Rick
What do folk think about this new Spray on glass technology
Seemingly it can be used on anything, including food!
"Now all we have to do is to go find a typhoon and do some testing.
–B.G.–"
Holding a piece of fabric over a high pressure garden hose
will give you a good indication of waterproofness.
A Gore ptfe or a 2 ounce urethane coating or a cuben fiber
will not let any water through.
A 1 ounce coating of urethane or a 1/2 ounce coating of
silicone may let a drop appear.
A .25 ounce coating of silicone or urethane will have a
few bubbles and droplets appear.
A simple DWR will have small sprays come through the fabric.
I haven't tried Epic treated fabric this way.
Carter,
The eVENT rating is for hydrostatic head. It varies with the face fabric. Some examples are as follows:
30,000mm – http://www.hike-lite.co.uk/Bargains+Section/eVent+Halo+Stretch+Jacket.html
30,000mm – http://www.amazon.co.uk/Montane-eVent-SuperFly-XT-Jacket/dp/B000W0WTMU
All of the Montane eVENT products list their hydrostatic head rating.
Hi Dave
> A simple DWR will have small sprays come through the fabric.
> I haven't tried Epic treated fabric this way.
Once the pressure is high enough to overcome the surface tension feature, EPIC behaves just like a DWR treatment. After all, they are really identical.
Yes, tested on a Suter tester.
Cheers
See http://jwbasecamp.com/Articles/DryGear/
Although Jim' analysis was focused on dry sacks, his observations also have applicability to this thread's discussion of tent fabric's hydrostatic head. Note the third paragraph:
"LOW WATER RESISTANCE
As noted above, silnylon is waterproof, but only to a limited degree. Any "waterproof" fabric will eventually leak if enough pressure is applied either to the water that's attempting to penetrate from the outside, or to the dry inside surface of a fabric that's pressing against an external layer of moisture (the case, for example, with a stuffed sleeping bag that's pushing against the walls of a silnylon sack that's wet on the outside). A fabric's water resistance is usually gauged with a device such as this that's used to measure a property known as the "hydrostatic head". This factor reflects the maximum amount of pressure that a fabric can withstand before it begins to leak and is commonly expressed either as the height of the water column (usually in millimeters), or as the number of pounds per square inch of water pressure necessary to initiate that leakage.
As a point of comparison, consider that even the lightest of the commercially available polyurethane-coated nylon gear sacks have hydrostatic head values that usually range from 5,000mm to 10,000mm (note also that heavier-duty dry sacks intended for paddling use typically have much higher values).
In contrast, the hydrostatic head of standard weight silnylon, according to most manufacturers' specifications, is only 1 to 2 pounds per square inch, which translates (for consistency with industry conventions) into a range of 700mm to 1,400mm. In other words, standard weight silnylon, on average, is less than 15% as water resistant as even the lightest of the conventional coated nylons."
OK, I've ordered one. A brand new FirstLight in Nano Shield material. I have a six year old FirstLight in Epic, so I might be able to do some side by side tests.
Will start a new thread with my impressions once the tent arrives.
Yay Kristin. Looking forward to the review – may I ask where you purchased it from?
I ordered it this Wednesday afternoon from basegear.com and it arrived by UPS a few minutes ago. That's less than 48 hours – not bad.
Basegear also had the best price as there was a 20% coupon and there was no sales tax nor shipping charges.
I'll post some first impressions on a new thread after work today.
Wow.
It looks green and no longer yellow?
Yup its a yellowish green, I think BD calls the color Wasabi. My old one in Epic is a bright yellow.
Very nice, Kristin. Do post a link to your new thread, once you gather your impressions + pics.
It looks awesome! Do we know if they are also going to offer the Lighthouse in nano? I'm hoping they do so I can continue to use my spare poles, cf poles, etc.
I emailed BD and i guess here is the answer to my own question: unfortunately, the only tents out of the line that are going to be continued on in the new fabric are the skylight, firstlight, and highlight.
This news about the new more waterproof fabric is fantastic. To those of you who have used or seen the epic versions in the past, which model is better, FirstLight or HiLite? More or less same weight and space in both, HiLite has a bit more refined design. Opinions?
Similar – the Hilight is side entry but also has a cross pole that provides optimal headroom throughout the width of the shelter making it a better 2 person shelter in my opinion.
Firstlight for the win. It is a proven clean design: see Bibler I-Tent, ID MK1 Light and MK1XL.
Thanks to Carter Young I had to go back and review an assumption which I determined was incorrect. Carter’s post said, “It seems to me that the flies used for expedition double-walled tents (MH Trango, TNF VE-25) are far less waterproof than you suggest. For example, Mountain Hardwear says on its website that the Trango 3.1 rates 1,500mm for the fly and 3,000mm for the floor.
MEC, which has always done a fine job listing tent specifications, says its Nunatak has a floor rated to 10,000mm and a fly to 2,000. When MEC previously sold Bibler and Moss tents, I believe that the Bibler Todd-Tex canopy was rated at 10,000mm and the Moss flies at about the same–Moss floors were I believe 15,000mm.”
Many vendors (Marmot, Sierra Designs, Eureka, The North Face (historically) list their tent fly hydrostatic head in PSI. Since they didn’t specify their test method, I assumed they used the industry standard ISO 811 or JIS 1092 test; so, I simply converted their PSI values to mm values and used the average converted number in my original post. What I discovered today is that many years ago The North Face listed the hydrostatic head of their tent based on the Mullen Burst (MB) test. For those of you not familiar with this test, it was originally designed to determine at what point cardboard boxes would catastrophically fail. Historically other tent vendors felt they had to use this MB rating system to be competitive with the North Face. Recently the North Face switched to the industry standard testing approach. Some of the other tent vendors still only use the old Mullen Burst number, some use both (without telling you which test is for which number) That is why my hydrostatic head value for PU coated 70D nylon was too high as Carter Young correctly pointed out. The correct value is approximately 5,000 mm. I updated my original post to reflect this number.
Conventional double wall tents commonly use outer fabrics with hydrostatic head rating from 1,200 mm up to 5,000 mm. As a matter of practice they don’t usually test above 5,000 mm for double wall tent outer material.
Kelty was the first tent manufacturer to use light tent flies. They found that the force dispersion angles and the separate inner tent allowed the occupant to be satisfied using a lighter coating even though water passed through the fly. What happens in a heavy rainfall is that water does go through the taut fly layer and runs down to the ground along the inside surface. A little will drip onto the inner wall but since it was not under pressure it will barely dampen it. Because the inner tent is breathable the moisture from humid air and from the exhalations of the humans inside would not condense on the inner tent walls but would pass out to the outer fly and leave the inner wall dry. They found that they didn't get double wall customer complaints with as low as a 1,500 mm fly rating.
You can do a Google search on any mm number such as “tent xxxx mm” and see many products in every category. The following is a list with just one example for each common hydrostatic head rating used in double wall tent flies.
1200 mm Big Agnes Fly Creek UL 2
1500 mm Sierra Designs Clip Flashlight
1800 mm SD Clip Flashlight
2000 mm Kelty Ridge 2
3000 mm Mountain Hardwear Viperine 2
4000 mm Terra Nova Laser Competition
5000 mm Coleman Helios XÂł
10000mm Bibler Todd-Tex (single wall)
25000mm RAB Summit Extreme Tent (single wall)
Single wall tents with hydrostatic heads less than the thresholds shown in the following table are vulnerable to misting whereas double wall tents inner layer effectively mask this phenomenon. The only light weight material that will avoid misting is Cuben.
Materials such as silnylon, Epic, and Nanotech, heavily rely on surface tension to achieve their protection. Smoke, dust, and aging cause a significant reduction in their functionality.
I guess I'm going to really miss the extra space of the LightHouse vs the Highlight. From what I can tell, the Highlight is similar enough to the lighthouse. I haven't owned a firslight but I've had a bibler i-tent and I have to say that for those sunny days, there is no comparison when it comes to venting– I'd rather NOT be in the firstlight/i-tent compared to the side-door design of the highlight.
Link to thread on first impressions of the new Nanoshield fabric tent.
According to this info:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=5260&startat=40
NEMO OSMO fabric:
Weight: 2.22 Oz/yd2
Water Vapor Transmission: 5618 g/24h/m2
Hydrostatic Resistance (Water Proofness) 123 psi
Where would that put it?
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