waterproof zippers on shelters

[AG]

apparently i’m the last person to learn that “waterproof” zippers like YKK AquaGuard are not, in fact, waterproof. ha!

my question is why do some of the high end DCF shelters (Duomid, Ultamid) use unprotected waterproof zippers. on pyramids this means that the drips go straight down into the inner/bathtub. i saw a sil Duomid with a flap over the zip — far superior if you ask me. but my DCF Duomid has no flap.

this seems like a design flaw.. and something that can be easily reduced/mitigated with a flap. what am i missing?

[Jerry Adams]

I use non waterproof zipper on mid.  I’ve made a number of iterations and haven’t had any desire to use a waterproof zipper

I think that the zipper is, like, on a ridge so water runs away from the zipper

Has anyone experienced drips coming through a zipper?

Occasionally I have to get in or out of my mid when it’s raining.  With the door open, a lot more rain comes through than any zipper drips.  You need to design your tent so there’s nothing important directly below the zipper and door.

Just one opinion, experience

[Jerry Adams]

and I haven’t felt the need to put a flap over it either

[Brad Rogers]

Interesting.  My DCF Duomid has a non waterproof zipper and a flap.

Back on topic – I’ve had several tents with waterproof zippers and no flap, including the X-Mid that I’ve used the past few years, including during an all day/night wintery mix (rain/sleet turning to snow) with high winds in WRR this year and the waterproof zipper didn’t leak.

[Dan @ Durston Gear]

The traditional way of keeping water from getting through a zipper is to use a regular (non-waterproof) zipper and then cover it with a flap. This doesn’t work very well for several reasons:
1) Flaps don’t reliably keep the water out. Flaps can blow open and expose the zipper in high winds. Some of the lighter flaps get crumpled (e.g. DCF flaps) and don’t fully cover the zipper even in gentle conditions. They do block most of the water, but a setup like this isn’t more waterproof than an AquaGuard zipper.
2) Flaps snag in the zipper. It’s very common for flaps to snag in the zipper – especially when you’re running to go pee in the night. The only way to alleviate this is to use a heavier/stiffer flap but then it’s heavier, which brings us to:
3) Flaps add weight. A heavy flap makes it less prone to blowing open and less likely to snag in the zipper, but then it’s heavy. A light flap is obviously lighter but then it doesn’t work very well.
4) It’s clumsy design. Instead of finding a way to improve the zipper to keep water out, a flap adds complexity to the design as a stop-gap measure for the problem. It would be more simple and elegant to simply have a waterproof zipper.

A YKK Aquaguard zipper is a more elegant solution because it makes the zipper fabric waterproof, so the complete zipper is very close to waterproof. The only way water can get in is by leaking through the narrow slit and then through the teeth. That can happen a tiny bit in pounding rains, but in these conditions a flap could easily be worse yet if it’s blowing open. Usually, a bit of leakage is not a problem because any water getting in is happening very slow and it will tend to run down the zipper and drip at the bottom. With my tents, we use Aquaguard zippers for a clean, easier to use, and lighter design and then the zipper panel is steep enough (60 degrees) so that water will virtually never drip off the zipper. Plus we have the zipper is located only over the vestibule, so even if there was a drip it would only land in the vestibule. We think this is a robust solution because the AquaGuard zipper is simple, light, never snags in the zipper, and blocks virtually all the water, and then any leakage does not affect the occupants. So essentially, the drawback of an AquaGaurd zipper can be mitigated with thoughtful design.

In my opinion, an AquaGuard zipper + steep panel + over the vestibule is the best possible design. Sure a 100% waterproof zipper would be better yet, but the only truly waterproof zippers on the market are a lot heavier and hard to use (high friction) like the YKK AquaSeal, so they’re not a viable option for a lightweight tent.

If you have a tent where the zipper is both shallower and over the inner like a traditional mid tent, then using an AquaSeal might be a bit questionable. Some companies with tents like this used to use both an AquaSeal and a flap (e.g. MLD, MSR) but I think they’ve all pretty much done away with the flap because it’s not really adding any performance yet adds weight and tends to snag.

One further note is that Aquaguard zippers don’t do well around a curve because they are higher friction. You get more wear on the zipper so it’s harder to use and can fail sooner. For that reason, some companies opt for regular zippers. For example, you’ll see Hilleberg using regular zippers with flaps on their models that have curved zippers but then when they have a tent with a straight zipper they switch to a nicer Aquaguard zipper. This poor performance around a curve is probably the main reason why regular zippers with flaps remains a popular configuration – that and AquaGuard zippers cost more.

[Rex Sanders]

Dan,

Thanks for the mini-course on zipper choice and design, and for an introduction to different YKK “water repellent” zippers. I was put off by their earlier designs, because the zippers were so bloody hard to open and close, and failed after a little exposure to sand and grit.

Seems like they’ve broadened the range and improved the product.

Buried in YKK’s confusing web pages, their AquaGuard product relies in part on a DWR coating for water repellency. As you mentioned: “This zipper is water repellent, not waterproof/watertight.”
https://ykkdigitalshowroom.com/en/item/40/

But as you said, with proper design, the AquaGuard is more than good enough for tent exteriors.

Interesting warnings under “Care Information,” but nothing most people would put their tent through:
https://www.ykkfastening.com/products/search/detail.html?pdid1=AquaGuard(R)+(Coil)

The YKK AquaSeal zipper is intended for rougher water contact sports, not for tents and rain jackets, with much more onerous care requirements than the AquaGuard. And heavier, and stiffer.

— Rex

[Dan @ Durston Gear]

I’m not sure what the DWR is for on the AquaGuard zippers, but the main coating is the PU coating on the fabric sides (‘tape’). That PU coating is what makes the fabric part of the zipper shiny and it seems quite robust. Sometimes it starts to wear off in heavily used zippers, but normally it would remain waterproof for the life of a tent. I don’t think I’ve ever seen it wearing off in a tent, but sometimes you do in an old jacket when someone is wearing it every day and taking it on/off multiple times/day so it’s seeing a lot of cycles.

So in my experience the AquaGuard zipper is only ‘water repellant’ because of the slight gap between the two sides. The tape itself is waterproof. It looks like the truly waterproof AquaSeal zippers also uses a similar PU coating on the sides – they just also add rubber edges to the teeth to seal the gap.

[Stumphges]

I’m intrigued by Jerry’s experience with normal zippers. Anyone remeber Richard Nisley’s suggestion of painting zips with silicone/solvent soluiton to make em waterproof? I can’t find those posts, but I recall him using that trick to waterproof the zips on Epic silicone-encapsulated jackets.

AquaGuard zippers are probably better than flaps, but I’ve had two fail on me in the past year and don’t care for their stiffness.

[AG]

helpful explanation, thanks. and i do like the x-mid approach: steeper angle and over a vestibule.

another challenge is integrating the zipper into the tensile structure. i like a taut pitch. these zippers are often being pulled apart under outward tension. i’d imagine this also makes the zipper less watertight.

of course some shelters mitigate this using buckles at the foot. but this doesn’t really address the tension across the whole face.

i guess the zpacks solution is just ditch the zip entirely and rely on a broad fabric overlap with an anchor toggle in the middle. plus locate the door on a beak not on a flat panel.

[Stumphges]

Doesn’t Zpack’s overlapping flat system result in horrible flapping in high winds?

[JCH]

“Doesn’t Zpack’s overlapping flat system result in horrible flapping in high winds?”

Not if the shelter is oriented “correctly” to the wind, that being the outer “overlapping” door panel being upwind.  In this orientation I easily survived  a night with gusts of 25 mph.  If oriented the other way round the outer door panel becomes a giant air scoop. If attention is paid to current and near term predictions of wind direction, there is generally no problem.  When the wind is swirling, or changes direction markedly overnight, it can be a real bummer, but then nobody ever claimed the Duplex was good in very windy conditions.

There are pros and cons to every design.

[DWR D]

“Not if the shelter is oriented “correctly” to the wind…”

I get a chuckle out of this much cited trope. I don’t know about anyone else, but I orient my tent such that I can have my head uphill and my feet downhill. Wind?! Geez… it changes direction and is often unpredictable in the mountains. I would never buy a tent based on having to orient it to the wind. Nice words, but not practical or even practicable.

 

[Dan @ Durston Gear]

Using door clips instead of a zipper is a loss in overall rigidity/stability. Imagine taking a 3D tensioned shape and then cutting slits for doors in it. Here you are losing a ton of rigidity because tension can no longer run across where the slits so the whole shelter will deflect more in the wind and stress will be focused in specific spots rather than distributed. If those slits are bridged by a zipper, it effectively restores the original performance (provided the zipper doesn’t fail), whereas if instead of a zipper you use a couple clips, that only partially bridges the slit. With only 1-2 clips, tension can not be evenly distributed across the panels, so stress is more focused and the shelter is less robust/solid. For example, imagine a wind gust hitting from a direction that applies a force across the doorway and far from where one of the clips are – there’s no resistance here, so the panels pull apart until eventually the clips take the load. In this case there is more movement of the shelter and stress is more focused and potentially multiplied.

I’m not saying clips are not a viable option. For many 3 season tents I think they can be good enough and do save weight, but you certainly don’t see serious 4-season mountaineering tents using a couple door clips, even if the clips themselves are very strong. From a structural standpoint, the ideal solution is a continuous connection (e.g. a zipper) which can then be reinforced if necessary (e.g. zipper + buckle). We use #5 zippers which are quite a bit more robust than the commonly used #3 zippers so we’ve never had one fail. Other companies like TarpTent also commonly use #5 without buckles and that seems to work well enough that they switch to #3’s on their most weight conscious tents. Quite a few company even use solely #3 zippers (e.g. Locus Gear, Big Agnes) and seem to get along fine with that, so I don’t think there is a need for additional support but perhaps down the road we add optional buckles at the zipper base as an additional safety margin on some models.

Anyways, from a structural perspective I think a 3 season tent is fine with clips. The main reason we don’t use them is because they are less user friendly (hard to operate, 2 handed job instead of 1 handed, can’t adjust how far open a door is).

[Ross Bleakney]

I would never buy a tent based on having to orient it to the wind.

Right, but then you are probably carrying a heavier tent, or one with less room inside. Trade-offs.

 

[Roger Caffin]

My tunnel tents can survive a bad storm side-on to the wind, but I know they will be even safer if I point the end into the wind. They can survive without the side guy ropes when correctly oriented (into the wind). I know, because they have done so (100 kph). Ah, but the two upwind anchors are crucial: without them the tent can go ‘away’. For the snow I have four very good ‘deadman’ anchors which will NOT budge.

I would try quite hard to avoid camping on the windward side of a ridge: that is where the wind is worst. If I camp on the lee side my head will just about automatically be uphill.

Cheers

[Stumphges]

Flaps are a PITA, but one nice thing about them, if paired with a two-way zip, is leaving part of the zipper undone for additional venting. The flap will often be enough to prevent rain ingress.

[Chris R]

What about an internal flap?

[Roger Caffin]

Internal flaps won’t work because of gravity. The flap will fall away from the zip instead of lying on it.

Cheers

[Chris R]

Would likely work better on a tent with a near vertical door. Doesn’t really need to sit against the zipper, just needs to be there to catch any drips and guide them toward the bottom of the tent.

[SIMULACRA]

Richard Nisley’s suggestion of painting zips with silicone/solvent soluiton to make em waterproof?

Not sure if I got the idea here, or otherwise, but I cut out the light cover flap of my non waterproof zip several years ago due to it always snagging. Applied a 4:1 ratio mineral spirits to 100%silicone over the entire zipper fabric and overlapping into the stitches. Both sides, inside and out, made sure it saturated deep. The thin layer of silicone on the zipper teeth acted as a lubrication. Has worked very well for me

[SIMULACRA]

I get a chuckle out of this much cited trope. I don’t know about anyone else, but I orient my tent such that I can have my head uphill and my feet downhill. Wind?! Geez… it changes direction and is often unpredictable in the mountains.

ha! I was thinking the exact same thing. Often I feel like I’m actually choosing the campsite, but in reality, it’s choosing me. Alpine mountain tundra is often unpredictable, bumpy, un-level and never going to be 100% in the winds right direction.

oh, and I checked my notes. It was 6:1 not 4:1

[Roger Caffin]

Yeah, some alpine country can be a bit bumpy, but we find that camping in the lee of a patch of trees is good, and the grass is often softer there too.

(France, somewhere in the Midi.)

With a good tent you are not so concerned about the wind anyhow.

Cheers

 

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