Where is the bias-stable DCF for tents?

[Stumphges]

In the BPL DCF webinar, Ryan talks about how Dyneema strands are oriented at 0 and 90 degrees in the middle of the DCF composite sandwich. In the accompanying Podcast #2, a DSM rep mentions that DCF does, contrary to popular belief, stretch on the “bias,” or 45 degrees from the orientation of the Dyneema strands (45 and 135 degrees). What he doesn’t say is that this stretch is inelastic; I could be wrong, but I consider it deformation.

In the webinar, Ryan mentions that DCF could be made with Dyneema oriented at four angles rather than two (0, 45, 90, 135 degrees) to stabilize the biases, but that it would make the composite pretty heavy.

Unless I’m mistaken, 0.8 oz/yard DCF has twice the Dyneema content of 0.5 oz/yard DCF. 0.5 oz/yard DCF is not considered heavy duty, but is used in tents made by Tarptent (among others), who have a very well-deserved reputation for knowing what they’re doing and building quality tents. So 0.5 must be strong enough for most applications.

What I’d like to see is 0.8 oz/yard DCF with half the Dyneema oriented in the “bias” directions – at 45 and 135 degrees. It would be as strong at 0.5 DCF – not just in two directions, but in four, and probably, effectively, in almost all directions.

The difference between an MLD Duomid in 0.5 and 0.75 DCF, for example, is about 1.5 ounces. Having a pyramid with bias-stabilized fabric would be very worth ~ two ounces to me.

[Jerry Adams]

Yeah, it seems like that would be useful

Maybe something spun bonded like Tyvek would work.  In DCF.  Fibers going every direction.

[Eric Blanche]

DCF has been made in the high bias (HB) version as mention years ago by Steven Evans (suluk46). I can’t quite find the source but I assume this was something that is no longer produced as the acquisition from cubic tech may have changed ‘directions.’

 

Admittedly, I have not listened to the podcast but could this be the material that is spoken of?

[Stumphges]

Hi Eric, Yeah, I think “HB” was mentioned, but I hadn’t realized that this was/is an actual product line. Thanks.

[Dan @ Durston Gear]

“What I’d like to see is 0.8 oz/yard DCF with half the Dyneema oriented in the “bias” directions – at 45 and 135 degrees. It would be as strong at 0.5 DCF – not just in two directions, but in four, and probably, effectively, in almost all directions.”

If you actually did this it would be a lot stronger than regular 0.5oz. That’s because when you pull at 0 degrees you’d have the parallel strands (like regular 0.5oz DCF) plus the diagonal ones also helping. Making the material even stronger is good if you want extra strength, but it’s overkill if you just want to solve issues with tension on the bias. Usually what you want is the same amount of dyneema but distributed into more directions. Then instead of being very strong in certain orientations and weak in other ones, it would be consistent in all directions. It wouldn’t be as strong in any given orientation, but it would be more durable overall because a fabric is only as strong as its weakest link and this would improve that.

Bias strain can be a big problem for DCF tents because the material deforms (permanent stretch) on the bias which is not only weak but also causes delamination and micro tears as the adhesive and mylar layers are stretched. The most common example of this is the Zpacks Duplex, where it’s fairly common to see material failure near the corners and hear of users trying to reinforce this area with DCF patches. I’ll explain the the problem with how the Duplex is patterned not to pick on Zpacks, but rather to explain how to properly orient DCF.

With the Duplex, Zpacks has the material oriented so the dyneema strands run horizontal and vertical as you can see below. This puts the dyneema strands in line (good) with the seams running along the tops of the doors, along the ridgeline, and along the bottom edge (green arrows below). The problem is that there is also diagonal pull from each corner to the opposite peak (red arrow below). This leads to stretch and material failure, as often reported by real world users (see image in next post as a clear example).

You might say “well there are forces from many directions so it’s not possible to align the strands with all of them“.  Indeed, except there are other solutions. When you use DCF tape on a seam, that tape has strands running parallel so the tape stops the problem. Similarly, when you fold DCF at the edges of the panel it becomes quite a bit stronger since there are multiple layers. With the Duplex, the lines of tension along the bottom edge and along the tops of the doors are already reinforced by other of these methods, so parallel fabric strands are not that important there. It is good the fabric is square to the ridgeline is parallel since that has a ton of force yet no seam there.

To fix this issue, ZPacks could:
1) Rotate the fabric 45 degrees. This would fix the diagonal problem shown by the red arrow and not create new problems above the doors and along the bottom edge since those are already reinforced. It would create a big problem on the ridgeline with diagonal fabric there, so they’d also want to split the overhead panel into two halves to create a seam across the ridgeline. Like this, you’d have a very strong ridgeline (stronger than before) while eliminating the bias problems. A nice improvement to the lifespan of the tent for only 2 grams. The probably with this is that the fabric panel wouldn’t fit onto the roll of fabric, so you’d have to add seams. I think you’d need to split the end panel into two halves.

2) Add diagonal seams. If you’re splitting the panel into two halves anyways, you could instead keep the orientation as the current tents are but divide that panel into 4 parts via two diagonal seams forming an X. Those seams would stop the problem, but it would be more work to construct. This is basically what HMG did with the Dirigo. I suspect we’d see it from Zpacks too but the tent appears to prioritize cost/ease of manufacture over performance. A Duplex with these X seams and a ridgeline seam would be a big step up in lifespan/performance but definitely harder to build.

This brings us back to high-bias DCF: It would be an even better solution because the high bias DCF would solve the problem naturally so post-hoc solutions like additional seams wouldn’t be needed.  Certainly it’s a better material. I spoke with DSM about high bias DCF and they do still offer it as an off-the-menu option. The problem is that they don’t have the ability to produce it in-house. Their DCF assembly line can only do 0 and 90 degrees, so they have to outsource the production to a 3rd party who hand make it in tiny batches. The cost for DCF is already obscene, and then high bias DCF is about 4x the cost (over $100 per yard) so you’d be looking at a $2000 tent instead of $650. I’m all about spending more money to create a superior product, but that’s over the top. Ideally we’d see DSM improve their production abilities so they can produce this at a similar cost, but until someone comes along that wants to buy massive amounts of it I doubt it’ll happen. None of that is really an issue with my tents anyways because they already have seams on all the major lines of tension so the orientation of the fabric doesn’t matter nearly as much.

[Arthur]

This is what Dan is talking about. Zpack Duplex after about 50 nights.  Zpacks said this was “normal” wear and tear. Wow.  On all 4 corners.   I am going back to my Tarptent non Dynema, non disposable tent with hundreds of nights and still going strong. 

[Brad W]

@Dan would it not be prudent for every Duplex owner to reinforce the corners-inside and out- upon purchase? Or would that simply move the problem just outside the patches edge?

 

@Arthur that is bad. Are you pitching it unreasonably tight? The tent is supposed to last one thru hike, I didn’t think they meant the Long Trail..

[Dan @ Durston Gear]

Yeah that’s a very clear example of a bias issue. It also looks exacerbated by the Z shaped stitching and how the reinforcement patch is adhered. Normally the bias delamination would start at the edge of the reinforcement patch since the reinforcement would stop bias stretch, but in this case it’s starting at the Z stitching either because the reinforcement isn’t properly adhered or the Z stitching is focusing stress. DCF tents can last a long time but the details really matter. It’s way less forgiving than woven fabrics.

[Dan @ Durston Gear]

Brad: From a corner you can have either (1) dispersing stress where force from all directions converges at the corner, or (2) linear stress where the stress is in a straight line from the corner to some other point. With dispersing stress a corner reinforcement helps a lot because you reinforce the focal area and enlarge that reinforcement until the force is low enough where it leaves the reinforcement. However, with these Duplex corners the stress is largely linear. If you reinforce to 5″ it’ll delaminate at 5.5″ or if you reinforce to 15″ then it’ll delam at 15.5″ because that same force exists across the entire line of tension from the corner to the opposite peak.

I’m sure a reinforcement patch does help somewhat (at the very least, it can repair a damaged area until it happens again elsewhere) but the ideal solution would be to strengthen the entire line of tension. That could be done through changing the orientation of the fabric, or adding a seam across these diagonals. A 3rd option that I forgot to mention earlier but is quite practical is simply adding DCF tape across the entire line of tension. You’d basically add a big X of DCF tape on the end panels and you’d dramatically improve if not eliminate the problem. This would be more effective than just corner reinforcements. Probably a wise thing to do for Duplex owners.

[Brad W]

@Dan Thank you for that explanation.

[Arthur]

I pitch the tent snug, but not what I would consider excessive.  It has been thru a couple of small sized hail storms at high altitude, but no severe  wind storms that would stress the corners.  I try to stay protected in stormy weather.  I put DCF squares over the area on all 4 corners, but I still cannot trust this tent to stay together in a bad storm anymore.

[Jerry Adams]

Interesting information

A $2000 tent?  We can call that the Elon Musk tent. Or Bezos.

DCF tape across the fabric along the bias?  That’s sort of like putting a stiffening strip on the ridge of a mid.  Except that reduces dynamic stretching, thus better performance in the wind.  As opposed to deformation stretching and failure.  Great solution.

Just thinking about it, a regular mid doesn’t have any corners like that.  The force from the corner tent stake guyline tieout goes along the ridge seam, which is along the bias, but the fabric is folded over twice to make the flat felled seam, so there are a lot of layers of reinforcement.

I have had the stitches of the flat felled seam fail – the fabric stretches (along the bias) but the thread (polyester) doesn’t stretch as much so it breaks.  But, it’s not critical because there isn’t any sideways force (assuming the two panels are still sewn together at the corner.

With a ridge reinforcement strip this doesn’t happen.

I think this is all so obscure that most potential users won’t appreciate it.  They just want a cool looking tent with the latest material that costs a lot, but not to the Musk/Bezos level.  If it wears out after a while it doesn’t matter because they’ve moved on to the next shiny object :)

[Brad W]

Would adding a couple of diagonal seams on both end panels and possibly across the ridge really cost that much more? $100? Could the Duplex Pro not be a viable solution to the increased cost? I for one would pay an addition $100 for increased durability.

[Stumphges]

Dan, thanks for answering the question in the thread title! So DSM has not, over the past decade, added the machinery to make HB DCF variants to scale. Very disappointing.

After Eric mentioned Steven Evans and HB DCF upthread, I found a bunch of lively and interesting threads from 2010, involving Evans, Mr. Lawson, yourself, and others. These threads were all about DCF’s limitations, which were just being identified at the time. Here we are, more than a decade on, and HB, which, as you say, would solve a lot of the problems with DCF as we know it, is still absent from the market, leaving us with design solutions and workarounds that each have their drawbacks (production time, production cost) and all cost extra weight. Yeah, a real shame.

Arthur, thanks for posting that pic. A very dramatic illustration of the bias deformation underlying the subsequent delamination. We can see that the Dyneema fibers are no longer oriented at right angles to each other, having been dragged along the bias towards the tieout.

 

Dan, a couple questions, if you don’t mind, about reinforcement strategies and the need for them:

1. I’ve wondered for a while about bonded DCF ridgeline seams. “Traditional” sew + bonding processes would stabilize ridglines with DCF edges on or near the bias (i.e far from 0 deg or 90 deg), because the overlying or underlying reinforcement fabric will invariably be oriented with Dyneema fibers parallel with the seam itself.

But are bonded-only seams stable? Let’s say we have two panels joined as a ridge, with both panels oriented such that the Dyneema fibers nearest parallel to the seam are 30 degrees from parallel. So, bringing those two panel edges together, you have a seam where the fibers nearest paralle to the line of tension on the ridge are 30 deg from that line and 60 deg from each other as they cross.

Is that an unstable seam if joined only with a strip of tape between the two panel edges? Should seams of this sort be reinforced with a strip of DCF tape oriented parallel to the seam? Is the glue on that reinforcement strong enough to actually transmit enough force to stabilize the seam?

 

BTW, do you know how Locus Gear do their seams?

 

[Dan @ Durston Gear]

Jerry: Yeah mids and most trekking pole tents don’t have unsupported lines of tension on the bias. With a trekking pole tent, all the major lines of tension run between the stake points and/or peaks (e.g. from a stake point to a peak, between peaks, or between stake points). With a single peak tent (e.g. mid) it would virtually always have a seam running from each stake up to that peak which divides the canopy into triangles where there are no unreinforced lines of tension. For example, the HMG UltaMid has all the corner edges on the bias which would be a big issue except they’re all seams and thus reinforced so it’s not an issue.

With a dual trekking pole tent the canopy might be divided up into triangles, but it might have rectangular panels (like the Duplex) where you have this problem. When the peaks are offset like the X-Mid and Stratospire then the canopy is all triangles, whereas when the peaks are square to the fly like the Duplex and SMD Haven Zero-G then you wind up with those rectangular panels with bias strain running diagonally across them. Those panels can be divided further into triangles, but often it isn’t done for cost and weight reasons.

Brad: With seams you’re looking at about 2 grams of extra weight per yard (for the tape and seam allowance), so if those diagonal seams are 2 yards each and you have 4 of them (2 per side in an X) then you’re looking at 16 grams – that’s a decent weight hit for a tent that is shaving every gram.

Adding those seams may not make sense though compared to just adding DCF tape as reinforcement. Why cut the fabric to tape it back together stronger when you could just not cut the fabric and add the tape. That would be quite a bit quicker to do and I suspect even lighter and stronger.

And then cost is hard to say but the tape and extra labour would add roughly $10-$20 in costs, so it could bump the price $20-$40. Probably on the lower end of that to just add the tape, but on the upper end if you’re actually cutting the panels and taping back together.

[Jerry Adams]

But the problem with a regular mid is headroom.  The sides angle in at the top so you end up hitting your head against the inside (which can be covered with condensation).

I like your solution with the two poles.  And I like your solution with the added DCF tape to solve the bias problem.

I have a side guyline, attached to the tent about even with where my head is.  It pulls out the fabric to give a little more headroom.

Maybe some day I’ll have to try that with the two poles diagonal.  I could buy yours, but then I’d be deprived of doing another project.

 

[Dan @ Durston Gear]

Stumphges: A ‘bonded’ seam can refer to a few different things, since the term gets used for any seam that isn’t sewn. Some bonded seams may use only adhesive (via double sided tape or glue) between the two adjoining panels, whereas other ‘bonded’ seams involve DCF tape. A common approach is to put adhesive between the two layers of fabric, but also slap DCF tape on top of that seam on one or both sides.

When you have a bias problem (a line of major tension running along the bias), then you have a wide range of potential solutions. The simplest is to rotate the fabric orientation to avoid the bias problem but that might not be possible if it creates bias problems elsewhere or the rotated panel doesn’t fit onto the roll of material. If you can’t avoid the problem by rotating the panel, then you can reinforce the line of tension either with DCF tape as a surface reinforcement or via a seam. I haven’t tried it, but I expect DCF tape will work as a surface reinforcement in the absence of a seam because it’s pretty common to have sewn seams with DCF tape where the stitching would quickly rip out without the tape and thus the DCF tape is essentially doing all the work (e.g. Zpacks).

Simply creating a seam will improve the situation even if the seam is only sewn or glued (no DCF tape) because now there are two layers of fabric to resist the stretch instead of one. It’s better but not great. If that seam also involves DCF tape then it’s improved quite a bit further yet since now you’ve gained parallel DCF stands. I consider that a complete solution. Another complete solution is to rotate the fabric on at least one side so that one of the two panels provides strands parallel to the seam. We do both on the X-Mid Pro. When we can align one or both sides of the panel with the seam then we can create a seam with only adhesive, whereas if the seam is on the bias then we use DCF tape to support. The latter is a bit heavier so I prefer the former but it’s often not possible since 2 out of 3 sides of a triangle tend to be on the bias (unless it’s a right angle triangle).

So to answer your question, I wouldn’t feel great about a ridgeline on the bias if the only reinforcement was a seam with stitching and/or adhesive (no DCF tape). I would definitely add DCF tape on top of this seam or rotate the DCF on at least one side, but it might be ‘good enough’ that some applications can get away with it.

Your other question was about where the Locus Gear bonded tents are made. The answer is that they are built at the same factory that builds almost all the good DCF tents on the market today. The same factory builds the DCF tents for Locus Gear, Durston, TarpTent, Gossamer Gear, and Big Agnes. Everyone uses them because they are the best. They have hot bonding equipment that uses DCF tape and double side tape, where the hot bonding equipment provides a stronger and more temperature stable bond than room temperature applied tape. It’s quite a bit more robust than the smaller shops building in house, although those seams can be good enough so the point may be moot.

[Stumphges]

Thanks, Dan. Much appreciated. Here is a photo of the tent I was thinking of when I asked about the 30 deg/30 deg ridgeline seam:

This was made by Jumperhome Studios and the ridgeline seams are bonded with tape and not reinforced in any way. Maybe the angles are more like 20/20.

To reinforce seams like this to prevent bias deformation, is best practice to apply DCF tape that is wider than the seam to get some overlap on either side of it? Or is it sufficient to apply DCF tape of the same width as the seam itself.?

Also, how would you go about applying DCF tape to the seams of a fly that is already built?

(These are some questions I was going to raise with the tent’s maker, who was still refining his techniques and processes, and was pretty open-minded. Sadly, he passed away in August. So I’m trying to figure out how to make this tent last a long time.)

 

[Dan @ Durston Gear]

It looks like a nice tent. So it uses double sided tape but not DCF tape? Hard to tell how the fabric is oriented in that photo, but since the triangles are narrow (acute peak angles) if the fabric is square to the ground then it’s not that diagonal to the stands on the seams to the peak.

If it is only double sided tape then yes you may prefer to reinforce further on the seams to the peak. I’d use DCF tape wider than the seam so it sticks to both panels (likely 1″ tape). Put that on the outside. Really though since there’s so many seams to the peak to share the load and they’re not too on the bias, adding additional DCF tape might be overkill and will add a fair bit of weight at 2 g/yd.

[Stumphges]

Dan, many thanks or your opinion. Yes, the ridges are bonded with double-sided tape and without additional reinforcement. And yes, the panels is square to the ground. The ridges appear to be about 20 degrees from 0, so about 40 deg from each other.

Yeah, adding all that tape will really add up the grams. If I knew I could get a replacement I would not bother, but given that the maker is no longer with us, I’m tempted to try to make it last. That’s the thing with DCF for me – these structures are impermanent, even ephemeral.

There is something very reassuring about a sil/sil fabric’s elasticity. Even a bad pitch will be forgiven, both on the day and long-term. With DCF, stretch the hems too tight and pitch it with exaggerated ridgeline curves only once and, well, you may have a permanently altered structure. Thus, really, the need for HB DCF, for there is no way to reinforce the bias everywhere it is being strained.

Final question: When adding ridgeline reinforcements to cat cut seams, how does one apply so the reinforcement matches that cat cut? Laying the seam on a flat table won’t do, as the reinforcement will then be shorter than the original seam. I hope you get my meaning. Not having built a DCF tent myself, the cat cut part of things is very hard to get my head around.

 

[Jerry Adams]

One way to make an octagonal tent is to make the side panels a little longer in one direction:

Only make it more than 3 inches.

I do the 3 inches to keep the edge on the ground all the way around.  Sometimes, you’ll see the sides of a mid a couple inches in the air, when the corners are next to the ground. Then, stuff can blow under the sides.  (except it’s such a minor problem it’s not a big deal, maybe more aesthetic)

But the 3 inches is a little longer than needed, which is maybe 2 inches, so I pull the out a little, going slightly from being a square, to an octagon.

Maybe 4 or 6 inches would make it more of an octagon.

Then, 4 ridges would be on the grain, and 4 ridges would be on the bias.  Put a stiffening strip on the bias ridges.

Maybe easier to lay out on a roll of fabric with less waste.

[Jon Solomon]

I think that is basically what the Aricxi Walker does. Makes a sort of rectangular octagon.
It’s a nice design though a bit heavy for one.  Quite wind resistant, as I’ve heard.
Maybe some users here could pipe in.

I have a Jumperhome Mountain House 2P, similar to what was pictured above. Used it above treeline in the Pyrenees this summer and was impressed with its wind and storm resistance. The shelter hardly budged in the face of a violent hail thunderstorm.

Back to your discussion about DCF’s “dirty little secret,” bias and stress deformation.

[Jerry Adams]

nice looking tent and nice scenery

looks like it’s made of strips that are about 1.5 feet wide?  I wonder why they do that.

side guys are slightly below the mid point.  On the ridges.  That’s another question, where should they go or are they even useful?

[Jon Solomon]

That’s beneath the Tuca de Mulleres in the Posets-Maladeta National Park. Lots of breathtaking scenery there. It’s also home to the highest peak in the Pyrenees.

The strips, which are effectively triangles as Dan noted, are what form the octagonal shape. The ridgelines are cat cut. Situating the guylines along the “seams” (which are bonded, not sewn) is not only stronger but better in the sense that it minimizes stress. I didn’t deploy the guylines in that storm but used them later in another howling storm. Only took four guylines to make the thing rock steady. I think that under 30 mph and possibly higher (I don’t have an anemometer) it doesn’t even need guylines for stability. And stability here means basically no deflection whatsoever.

My user experience leads to me think the octagonal shape has got to play a huge part in this. Now that Jumperhome is defunct, nobody is making these anymore. I’d love to see one in this high tenacity 30D silpoly or this diamond cordura 30D silnylon. I think it would unbeatable in terms of strength and more reliable/easier to pitch/less expensive/longer service life than DCF. Using a 20D silpoly from RSBTR would probably bring the weight down close to 0.8 DCF but I’m not sure how the stretchier 20D would work. The one in the photo weighs 415g with huge interior space. It’s somewhat of a pain to fit into the octagonal shape given a center pole set up, but I’m willing to make the trade off and used a Yama Gear Wind Bivy inside for bug protection. The design would be even lighter without the snow skirt and additional interior reinforced stake loops for set up on snow. Certainly under 400g.

The one drawback of this design is that it relies on the door being closed to get the right tension all around the structure. You can’t really see it in this photo, but with the front zipped open, the whole perimeter loses tension.

[Stumphges]

Just to add to what Jon has said, the octagonal tipi shape is quite awesome in wind. I’m a sucker for octagonal tipis. I have five of them, all made by Chinese companies. Eight has special significance in Taoism, but the other reason these companies favor octagonal tipis is that they are using them on the Himalayan plateau.

Aside from the DCF tipi pictured above, the others I have are all in 20d silnylon that I do not think is of the same quality used by promiment mid makers. Nevertheless, these tipis are rock solid in wind. In addition, as I’ve mentioned before, these octagonal tipis with their inferior silnylon are the only sil shelters I’ve seen that do not sag when wet and cold.

This, I believe, is why: I think radial symmetry in a cone shape (a tipi, in other words) increases circumferential tension. In other words, the more obtuse the corners are on a mid, the better tension transfers from one panel to the next, circumferentially. Kevin Timm from Seek Outside once wrote on this forum that he’s noticed that the greater the number of panels a mid has, the less need it has for cat cuts.

So these 8-sided mids don’t really need cat cuts, but if they are present it becomes even easier to get the panels super taut. And the key to getting woven fabrics taut is to stretch them on the bias. I think cat cut tipis stretch the bias extremely, to the point that the fabric may be a bit overstretched. So when you add cold and wet, the fabric might (must?) sag, but that sag isn’t even noticeable becauese the fabric was under so much tension before the temp/humidity change. Anyway, that’s what I think is going on (and I’m leaning on the Farrington hypothesis.)

 

But because this design stretches the biases of the fabric so naturally well, it is maybe the best design for silnylon and maybe the worst design for DCF. With the currently available DCF, which is stable in only two direction and almost begging to deform in all other directions, a design that tensions the bias really well is really a design that deforms panels really well. But I have not owned my DCF tipi for that long; maybe it will hold its shape OK.

But one thing is certain: this design would be a bomb shelter made with high bias DCF. It would be very easy to get extreme tension on the panels, and as you can see in the photo Jon posted, when the tent is tensioned well, it pulls into a cone shape that spills the wind extremely well. So super-aerodynamic with super stiff fabric that is NOT prone to deformation. I guess we can only hope. Or mobilize market pressure.

Jerry, the vertical lines you see in Jon’s tent are a feature of the DCF fabric. You’ll see them on all DCF tents. Sometimes they are vertical, sometimes horizontal – just depends on how the maker cuts and orients the panels. I think they are areas of increased Dyneema strand density, but I don’t know their function. They are not seams.

Obviously, single pole tipis are no good in terms of volume/footprint or headroom/footprint. A round shape is ill-suited, generally, to lying rectangular hominid bodies. Dan’s X-Mid is far superior in terms of livability, comfort, dry entry, etc., etc.

But the Jumperhome Studio Mountain House 2p might have been the most wind-worthy ultralight shelter ever made.

[Author]

Posts