What HH do you need for a tent/tarp fly to be waterproof in nasty downpours?

[Murali C]

Here is a table showing the HH values of some tents/tarps:

It seems like many of the most used tents on the long trails like PCT/AT/CDT are the Nemo/Big Agnes tents which seem to have just 1200mm HH. Reading the reviews of these tents, folks have used these in heavy rains without any issues. Reviews include usage on AT as well – which tends to have lots of rain.

There are some who claim that this is not enough. This is the bare minumum and tents with 1200mm will not stand to heavy rains.

So, what is a good number? And why would manufacturers make tents with such low HH if it is going to leak in heavy rain – if 1200 mm is indeed low enough to cause leaks in heavy rains. I mean these tents are in the 2 lbs to 3 lbs range – adding 2 to 3 ounces to bump up the HH should not make a difference to weight.

[Monte Masterson]

3000 mm

MTN silnylon 6.6’s with pure silicone on both sides, and no PU either as a mixture or on one side silicone and the other PU are superior. There’s a reason why MTN 6.6 cost twice as much as all the materials that aren’t. Stonger tear strength too. MLD’s 20D and Tarptent’s 30D are quality 6.6 silnylons. All Tarptents are rated at 3000 mm to 5000 mm, even the new 20D silpoly Henry is now using on the Preamble and StratoSpires.

A PU/silicone mix does allow for a fair HH at a slightly lower weight though, and it’s considerably cheaper to produce.

I know Ron at MLD tests every roll with his own machine to make sure it’s up to standard, and I’m sure Henry S has similar quality controls.

Most of MSR’s tents are rated at 1200 mm. Same with Big Agnes. What DWR D stated about tent waterproofness and how most people are fair weather backpackers (in WP Bivy thread) is absolutely spot on. With the exception of The MSR Hubba NX, Big Agnes and MSR tents are notorious for wetting out in sustained heavy rainfalls. And they are your biggest sellers in today’s US tent market. Heck, 3F UL Gear is a lot better than they are and way cheaper.

[R L]

Why then does a silnylon still sag when the HH is high?

[DWR D]

I would add, in addition to most people not actually using their tents in heavy rains, most people will not go to the trouble of complaining… and/or, by the time they realize that their tent leaks, it is out of warranty, so they don’t bother complaining. And… I don’t imagine Nemo or MSR or others would be likely to publish the number of complaints, if they even keep track.

[Dan @ Durston Gear]

Ratings aren’t quite as simple as they first seem because all they show is the performance for the new material. Any of these materials are quite waterproof when new since you only need about 600mm to reliably keep the water out, but since coatings degrade you want to start much higher than that.

Even for two fabrics at 5000mm, one might be durable and deeply impregnated while the other is thinner coatings that break down more quickly.  Because of this, I think the new ratings are pretty meaningless and it is the worn ratings that really matter. What we do is wear test the fabric and then we provide the spec for a substantially worn fabric. So I do say 2500mm for our X-Mid fabric because I think it is a more useful spec, but that is not comparable to the other specs in your table because ours is the worn rating and the others are the new ratings. When new, ours is closer to 5000mm.

With regard to coating types, it is a common marketing tactic for companies to say “we use X because it is better but expensive whereas other companies don’t because they are being cheap“. This makes for effective marketing while conveniently ignoring the actual reasons why other companies make different decisions. For coatings, the decision on which ones to use has almost nothing to do with cost. For a longer discussion on this topic check out the coatings section of my article here:
https://durstongear.com/materials

But in short, silicone is great because it adds strength and works well but you can’t commercially seam tape it. PU can be seam taped but weakens the fabric, and then PEU is a nice option because allows seam taping like PU yet doesn’t degrade the strength nearly as much (it can be a slight negative or positive depending on the formulation). So strength and the ability to seam tape are the main considerations, not cost. A few companies do mix coatings (e.g. Sil and PeU) and apply them to the same side of the fabric, but that is not typically what Sil/PeU means.

If a company is a smaller cottage shop and doesn’t have the expensive machinery to seam tape anyways, then of course it makes sense for them to use sil/sil and require that their users seal their own tents. That lack of seam taping equipment is the real reason why small cottage companies almost exclusively use sil/sil but “we don’t have the equipment” isn’t a very satisfying reason to a customer so typically these companies will give some other reason. When you get into more advanced manufacturing and do have access to seam taping machines then it makes more sense to use Sil/PeU because it is very similar in strength to Sil/Sil but allows for seam taping on the PeU side which customers appreciate much moreso than having to self seal their new tent. That’s why almost all the bigger companies use Sil/PeU. It’s not about cutting cost, it’s about creating a tent that is ready to go.

The idea that companies using sil/sil are doing something more expensive is not correct. The cost difference between different coating types is typically in the pennies, whereas seam taping is expensive ($5-$15) so almost certainly seam taped Sil/PeU tents are more costly to produce.

[DWR D]

Dan,

Thanks for your informative answer.

Two Questions come to mind:

1) Do you think the Nemo and Big Agnes tents listed as 1,200 nn are adequate protection for an intense rain storm? Do you think that fabric will leak?

2) Interesting that you start with 5,000mm rated fabric and wear it to 2,500 for testing. How much time/wear does that take to cut the ratings in half? How much time would it take for a Nemo fly to go from 1,200 to 600?

thanks

DWR

[Sam Farrington]

Agree with Monte 100%, except did not know of the issues with MSR and Big Agnes tents.  Did order a BA tent once, and when it came it weighed over half a pound more than spec’d, and that was without stakes or stuff sacks.  Called them and was informed that the guy lines had to be included in the weight.  Were that so, it would take climbing rope to push the weight to what it was.

Also agree that aged or ‘worn’ fabrics will have far less HH than when new.  This was shown by the tests done by Stephen Seeber, and earlier by Richard Nisley and reported on this site.  And how a tent ages depends on how it is treated, and for how long; so there is no simple answer.  So if I have access to an HH tester, I just look for at least 1500mm HH AFTER simulated aging.  If I don’t, I just squeeze water through the fabric, and often, the differences show the quality or lack thereof.

Another issue as I found to my dismay is that HH varies substantially from roll to roll produced by the manufacturer.  This was shown by test results furnished by Stephen Seeber.  He attributed that to “QC;” or quality control.

To further complicate matters, many tent vendors just low ball their HH to avoid conflicts.  So for tent buyers, all you can do is to rely on the reputations of  tent makers; which is what we have to do in a market economy generally. Wish there were a better answer, but don’t see it happening.

[Murali C]

I guess I don’t understand the motivation of these manufacturers who make 1200mm tent fly’s. I mean, these tents are pretty heavy at 2 to 3 lbs and are expensive as well.  So, it seems like it should be trivial to bump up the HH to 3000 or whatever – would it not? I thought these companies have very good reputation and just don’t see their motivation to put out products that are going to fail in bad rains. Its not like they are pushing the weight envelope.

While I was reading reviews, there were both positive and negative reviews – so, I don’t think these companies are eliminating negative reviews. Folks take them on thru’ hikes all the time – especially the Big Agnes and Nemo tents. Some of the reviews say they completed their AT hike etc. And on thru hikes, you don’t get to choose your weather as it is 4 to 5 months long – you just take whatever you get in terms of weather. I am just surprised that these tents could be failing in heavy rain. I disagree with DWR that people will not write their bad experiences…I think the opposite would be true – most reviewers would write their negative experiences rather than their positive experiences.

Anyways, would be interested in hearing Dan’s take on the DWR’s follow up question.

[Monte Masterson]

Of course there are good tents produced in Asia, just look at SMD, Durston X-Mid and 3F UL gear. But if you knew how little it really cost the mainstream companies like Nemo, Big Agnes and MSR to get their tents cranked out in China you’d probably laugh. Remember they are wholesaling to retailers like REI, Campsaver, etc at about half of MSRP. MARKETING is the number one reason for their massive sales.

And God only help you if you get caught out in a major blow in one of those flimsy mainstream UL tents. With 35 mph plus winds and rain shipwreck is almost guaranteed. And as far as the AT, most backpackers gravitate to the shelters and hostels anyway, with few facing real challenging weather conditions.

[Murali C]

Here is a video of Miles gear bivy – Uber bivy with a HH or 1230 mm. He hoses it with water from a pipe….no leakage. Take a look. So 1230 mm seems adequate????? I mean look at the force of that hose!

[jscott]

I used Big Agnes tents for years. I was in a lot of torrential downpours, and some monsoonal storms that lasted off and on for several days and nights. Including being directly under thunderstorms at high altitude with little or no cover. With the Fly Creek Ul 1 I never had a leak. Actually, that’s always what I liked most about it. Bombproof. So….

[Murali C]

Allright! An actual Big Agnes tent user!

[jscott]

Allright! An actual Big Agnes tent user!

 

I’m a rebel. Always have been. bad to the bone. Bone dry, in that tent. that said, I moved on in later years.

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