Delta Karo Step?

[R]

Are squares the best shape to use for a karo step? What about triangles?

To answer this question, let's begin by identifying the performance aspects we design for.

Loft is probably the most important. This is a function of cell size: the larger the cell, the bigger (thicker) the bubble it will form when stuffed with down and hence the greater the loft. But what exactly do we mean by 'cell size'? At first glance we might say it's area. But consider the 'cell' of a continuous baffle. In that case loft is determined by width, the distance between the seams, rather than the total area. So I propose that the relevant dimension when considering loft is minimum cell radius; the shortest straight line that can be drawn from the geometric center of the cell to any point on one of its sides.

The next aspect is down mobility. One factor of this is again cell size, and again, I propose this is really minimum diameter. If a down bubble is too big, the down is too free to slosh around resulting in uneven distribution. Another factor is the mouth length of the cell. Shorter mouths (smaller holes in the corners of the cells) reduce down mobility.

So I propose that by holding minimum cell radius and mouth size constant, we can compare various cell geometries.

Here are the relevant values for the popular 12/6 square.

Side length = 12
Seam length = 6
Area = 144
Total seam length = 24
Total seam length / area = .166
Total mouth length = 16.97
Total mouth length / area = .118
Seam count / area = .0139

Here are the relevant values for two equilateral triangles with the same minimum radius as the square (6). Both of them have a seam count / area ratio 42% lower than the square. That's a definite win in assembly effort. They also both have a higher minimum radius on the 'interstitial cell' defined by the mouth lines. This means the cold(-ish) spots where cell corners meet will be warmer.

This design comes very close to having the same total mouth length / area ratio as the square.

Side length = 20.78
Seam length = 6.93
Area = 187
Total seam length = 20.79
Total seam length / area = .111
Total mouth length = 20.79
Total mouth length / area = .111
Seam count / area = .0080

This has 33% less seam length / area. That bodes well for warmth in a sewn-thru design, and saves weight in a baffled design. However, when drawn on paper it looks way too open for good down stabilization. In practical terms, the weight savings on a 1.5" finished baffle made from .7 oz / sq.yd. bug net is about 3 grams. The warmth improvement for sewn-through designs is probably a little more substantial than that, but still probably not huge and difficult to quantify.

This design has the same mouth size as the square and some friendlier dimensions to work with (no crazy decimal values).

Side length = 21
Seam length = 12.5
Area = 191
Total seam length = 37.5
Total seam length / area = .196
Total mouth length = 12.75
Total mouth length / area = .067
Seam count / area = .0080

This has an 18% higher seam length / area ratio than the square, but the drawing looks like it will have down mobility much closer to the square.

Clearly some experimentation is in order to calibrate design dimensions against down mobility, and in sewn-through designs, warmth impact. However, the greatly reduced seam count is a clear win.

Below are sketches of the square design and both triangular, or 'delta' designs. Sure enough, the delta pattern has 29 seams to the square's 49 – 41% less.

Curious to hear your thoughts and critiques.

(Note – I have yet to make a quilt or bag.)

12/6 square karo step:

21/7 delta karo step:

21/12.5 delta karo step:

[And E]

I like your idea! You should totally make it and let us know how it works! I may make another quilt and try that if it works out well.

[Jordo _99]

I'm actually just finishing up the sewing on a 9/6 Karo quilt. I intentionally opted for a 9/6 because I thought that 12/6 would allow for more shifting than I wanted (and 9" divides well into 54".

I'll be making a few more in the coming months so I'll be sure to watch this thread closely.

I would expect that this could work very well but one concern would be sewing it…sewing the squares has been challenging but I suspect that's due to the tighter configuration I'm using. My first thought was that triangle karo would be harder (60 degree angles vs 90) but if you sew them in the correct order you'd be working with 120 degree angles…so as long as you're smart about it, sewing would likely be easier.

I'll post a bit more later today. Just getting to work and have some stuff to take care of first.

[Tim Marshall]

After making KARO quilts for over 3 years and having some success and some failures I'd recommend 10/6 over 12/6 or even over 12/8. (9/6 seems a bit tight but no shifting issues i bet) Tighter squares will give better performance. Our underquilts use 11/6 but by design the gravity pulls the down where you need it on and underquilt but away from where you need it on a top quilt which is what lead us ultimately to move to a new baffle system on our top quilts. For DIY you can do a 10/6 and have a nice quilt but for production it was getting too time consuming and complicated where the vertical or shiftless baffles systems work with less fuss and are much faster to assemble. Stuffing the KARO sure is nice though.

The triangles sure are interesting.

-Tim

[Jerry Adams]

to prevent sloshing around of down, I think cell width should be twice the loft

maybe twice isn't the perfect ratio and a sligthly different value is better. Probably a lot of range in that ratio is okay too.

the point is, if your loft is bigger, then cell size can be bigger

maybe hexagons are better

[Adam Kilpatrick]

There is probably an ideal loft/cell length ratio (or curve), and this probably varies depending on direction and location on the bag. Eg it could be that over the torso, cell length can be quite long in the vertical direction, while the horizontal direction its better to have them short…this bears out in the vertical baffle designs seen in many high end bags. However the actual dimensions of each of those vertical baffles, their precise widths lengths and angles, likely has a different number depending on where you are in the arc from one side to the other. My guy feeling says that you want tighter (x dimension) spacing towards edges, but I could be wrong, it could be the opposite. That may also depend a bit on whether one is a back or side or stomach or combo or fetal or turner…

All this would play out on a triangular or delta type karo pattern, where we assume that things don't have to be square. For example, in the torso, you could leave out the horizontal baffles of the triangles in some places to create diamonds in that run in the vertical direction. Towards the edges you could make them smaller, with longer baffles/shorter holes. You could start changing the angles too so that there is less horizontal vs vertical etc.

I like where this thread is going.

[Jerry Adams]

Marketers like to come up with some cool different idea like maybe spiral baffles.

Differentiates their product from others. If they're clever marketers, it can "go viral". Generate a bunch of sales. Maybe has no performance advantage. (not to be dissing spiral baffles if there is such a thing : )

If you did computer modeling maybe come up with better baffle design. Simulate human moving around, down moving in baffles, human fluffing and redistributing down. Calculate thermodynamic effects. Minimize cost or weight to provide a given warmth.

[Bob Gross]

I have an idea for baffle design, the Mobius baffle. Instead of having an inside and an outside, it would have only a single side. That would either reduce material or reduce labor.

How would I actually produce that? I don't know. I'm baffled.

–B.G.–

[Ryan Smith]

Well done, Bob.

I like that there is potentially less sewing. Sewing Karo baffles is pretty terrible. However, my initial thought is that this design will not control down as well as a typical box style Karo without making the mouth areas really tight. (I think thats what Adam is saying also) Maybe can make them sufficiently tight and still save some sewing. This is all from the perspective of a restless side sleeper. Trial and error i suppose. Hopefully I'm wrong. Make it with some cheap materials and see how it goes!

PS – I love the thought process that you used in determining the design. A lot of things are done through trial and error, but by using some critical thinking you've removed a lot of variables.

Ryan

[Gordon Gray]

I like your data and options for determining seam length.

I was thinking about all this the other day when drying out my down bag and separating the clumps of feathers within the long, but semi narrow, baffels of a Kelty Cosmic. (damn cat pissed on it).

[Adam Kilpatrick]

Yes, I think the two most important factors will be mouth size and also maximal distance between baffles (MDBB).

MDBB is important, as the larger the distance between two baffles, the less three dimensional control there is over the inner and outer fabric between the baffle, and thus, the more round the "cell" could become, thus increasing its potential volume to hold more down that should be in other areas.

The mouth size (MS) affects the rate of exchange of down between cells (DER).

If both MS and MDBB are large numbers, then your down is going to move about all over the place and not be even and where you want it. If MS is zero, then down stays in its baffle (like most normal baffled bags and quilts). If MS is infinite, you have no baffles! As MS gets large, again down "could" move between cells. However good Karo designs work because they have enough down density, AND MDBB is not too large.

To garantee that your down stays where you want it, mouth size zero, MDBB small. However, this is heavy due to increased baffle materials, stitching. So, the aim is to increase mouth size and MDBB up until the point where the DER is still very minimal.

I'm such a nerd. I'll stop now otherwise this will end up as a series of R scripts, lots of experiments with two or three baffled mini quilts, and, oh, further delay of my PhD submission.

[David Franzen]

in my experience, minimizing maximal distance between baffles (MDBB) helps more to reduce down shifting than mouth size (MS) does.

in one quilt i added really short additional baffles in the inner of each cell which halved MDBB. weight gain was about 2g for the whole quilt compared to karo baffles. i do not experience any down shifting at all. sewing it was a lot of work though.

[J-L]

I would think that minimizing the maximum distance a piece of down could travel before hitting a baffle would be important. For example, if a baffle pattern allowed for no direct path of travel greater than say 8 inches in any one direction (sort of like "Plinko" from the Price is Right), then down migration would be difficult. By staggering the baffles in a triangular or square design, I think you could achieve this.

[Adam Kilpatrick]

Hmm, yes.

There's also some kind of laminar flow resistance effect. So, on long vertical baffles, as long as the cross section of the baffle tube isn't too large, and there is the right amount of down in there (to full loft per weight) then it doesn't shift.

If the laminar flow resistance (not sure if I'm using the correct engineering terminology here) is strong enough in whichever direction, then, could there be almost no baffles? So, baffles that are say just a few mm across, but many of them, just to hold the inner and outer fabric together at the optimum distance? This is something that could be experimented I think. Of course its a huge amount of work to do, much harder to sew than a simple tubular baffled quilt.

I think the 8 inches in one direction idea is a good one too. 8 inches is probably conservative on the down control side, many karo quilts use much larger cell sizes than that, up to 14 inches (in the square direction, the angles are of course higher). It sounds like 10/6 karo works really well. So that's more like 10+ inches between.

On a contour shaped quilt, ie not a perfect rectangle, angles in the edges are introduced. So this makes it more sensible perhaps to have angled baffles in response.

One though I had last night while sketching on a graph pad, was that baffles that connect to the perimeter edge of the quilt are probably a waste, as they are over controlling the inner/outer at that point, and creating "corners". Corners are probably a waste if we agree that we can have mouths between baffles as long as they aren't too large.

**** Thanks to Rene, the original poster of this thread. This has really made me think (and want to build a quilt soon). ****

Getting back to the triangles hypothesis, looking at a patter like Rene did with 3 triangles across irked me too much. I guess its the lack of symmetry horizontally across the quilt; perhaps I'm a bit OCD! Would be interesting to draw up a 4 or 6 triangle across arrangement. Perhaps the sewn baffles could be shorter in response, or leave out some horizontal baffles.

Thought experiment for you:
-Imagine two pipes, both same cross section
-One pipe is perfectly straight
-Pipe #2 has some slight curves in it (say up to 10 degrees) a few times on its way down.
-Two metre height
-Put marbles in, all same.
-Which one flows faster?

*My thoughts are the straight pipe. The more curves in the pipe, the slower the flow. If the substrate is very liquid, like water, the effects are minimal. But they are there.

-So, if you do a vertical down baffle, for arguments sake on a sleeping bag rather than quilt, and you then sit up, thus making the torso baffle tubes vertical, down wants to flow down. If those baffles had some angle to them, perhaps there would be more resistance in this direction.
-Now lay back down. Those vertical baffles are stopping down flowing sideways to the edge of the quilt. If they are continuous that will always work. If they are karo, then the more perpendicular they are to gravity, the better they will work. But down is viscous. So they probably don't have to be perfectly perpendicular. They can probably be far from it, I'm sure at least 10-20 degrees from perpendicular.

So if you have an area of a quilt that you need to baffle, perhaps an angled baffle in the right direction will be more efficient overall for different scenarios than a perpendicular baffle.

[R]

Hey all,

Thanks for all the input – great to see a new idea resonate w/ an informed audience.

Adam – somewhere I think you mentioned super short baffle seams (just skimmed your comments and can't seem to find it).

That's a notion I was also playing with. The home decor people call it tufting – they do it to sofas and chairs. Basically a sewn thru karo w/ near-zero seam lengths. I crunched some numbers on this and you end up w/ about twice as many seams per unit area as a traditional karo, but 1/2" seams are easier to sew than 6" seams, and there's a big reduction in seam length and hence cold spots. However, this is based on a cell perimeter defined entirely by mouths, which will no doubt have greater down mobility, so this is only of speculative value in the absence of some prototypes.

Here's another approach for a baffled quilt. Start with length wise continuous baffles. But don't make them straight, make them zig-zag with 90-degree angles at the bends. If adjacent baffles mirror each other, the angles can touch forming square cells. If those cells are 12" on a side, like a typical karo, the width of the zig-zag is 8.5" and it only takes 6 to span a typical 54" shoulder width. And I'll bet if you use a mesh for the baffles w/ relatively large holes (something like this: http://www.califabrics.com/black-9-russian-netting/) you'd get enough down mobility to push it around when you fill it and to accommodate varying conditions.

So we're talking a square baffled karo with only 6 baffle pieces and 12 seams. A delta karo could take that down to 5 pieces with 10 seams.

I can't imagine there isn't a mesh hole diameter that will produce suitable down mobility – we just have to find it.

[Adam Kilpatrick]

Super short baffles, yeah that would definitely be interesting to test if you are going to run some tests. Yep, basically creating lots of mouths but with little overall seam length. I have a feeling that the key to this working with a superlight down quilt would be to optimise the orientation of each super short baffle. So even though they are say 1/2 to 1 inch, they still have "some" physical resistance to down flow.

I was thinking that larger a larger Karo system that sometimes has down control issues (as mentioned in forums) like 14/6 square, could be improved by having some of these super short baffles. Just one in the centre of each square. This would greatly reduce the potential for that square to overloft past its specified height. This then increases the density of down in that cell, which then reduces the chance of extra down migrating into it.

I'm struggling to grasp your zig zag concept (how it looks), might need a rough diagram.

Black Russian Netting. Kinky stuff, how do you sew it easily??? Be interesting to find out the weight.

[Roger Caffin]

Seems it could be rather tricky getting every little baffle correctly aligned on the second surface, which might make it completely uneconomic to make in Asia?

But my bigger concern is getting the down IN. How do you get all the down in place and uniformly distributed? Seems a shade tricky.

Cheers

[Roger Caffin]

Let's get really creative here and look at real alternatives. (Sewing those seams looks a bit horrible to me.)

Many years ago I made up some quilts which turned into another one of my MYOG articles. But I made one of the seams at the foot of the quilt just a bit too narrow, and the seam pulled out while I was in Europe. I was in my tent at the time, packing up for the day's walking, which meant I did not have a lot of time for repairs. What to do?

In my repair kit I carry some strips of UL fabric with double-sided tape on them, for emergency repairs. The strips are ~15 mm wide. I use 3M9845 'seam-stick' tape for this as it is supposed to make a 'permanent' bond. It works fine for me, but not on silnylon. The Coghlans repair fabric is similar but much heavier.

I aligned the frayed edge back where it should be and stuck some of this repair tape along the seam, and rubbed it down carefully. The idea was that this should hold until I could make a more permanent repair. Well, about 6 years later, the tape is still holding perfectly and I haven't bothered to do anything more. I haven't even bothered to try over-sewing the tape.

I wonder: could you use this same tape to stick the baffles to the shell, with zero sewing on them? To be sure, mistreat the baffles and they might pull off, but that probably also applies to sewn baffles.

What I do not know is how many washings this tape will take. So far it has taken one washing with warm water and down detergent with no visible change.

Note: the tape seems (to me) to work best on a NON-DWR fabric. The fluorocarbon coating of a DWR treatment seems makes it harder for any adhesive to stick. But this would need proper testing.

Cheers

[R]

Re. visualizing the zig-zags..

Here's one zig-zag seam:

/

/

/

Now here are 6 side by side:

/ / /
/ / /
/ / /
/ / /
/ / /
/ / /

Re. sewing netting. I'll bet ya could lay it down flat, put a strip of masking tape on top of it (the tape would stick to the lower layer of fabric thru the mesh holes) and sew right next to the tape. Easier than pins.

Re. weight – I don't know what that stuff weights (I'd imagine < 1oz/sq-yd) but this design has ~2.25x the baffle length of a 12/6 karo. It would take about 1 sq yd for 2" baffles on a typical 6' quilt. At 1oz/sq-yd for the netting, that's a penalty of about 2/3 oz against a bug net baffled karo – not too bad.

[R]

Roger,

Agreed on a little more difficulty sewing the second side of the baffles.

It sounds like your repair only loads the tape in shear. If you were to tape the baffles w/ a single strip, you end up peel-loading the adhesive. If you go to the trouble of double taping, I think you're flirting w/ similar effort to sewing. But you don't need this zig-zag design to try taping baffles (and a 100% taped quilt does sound kind of cool, even with the weight penalty of adhesive).

To fill this type of quilt, I'd leave the final seam gap equal in size to the open end of the plastic bag the down comes is, then temporarily tape the mouth of the bag to the open seam. From there you just push the down around as normal for any karo. Again, the notion is to find a netting that results in a down permeability on par w/ the mouths of a karo design.

[Roger Caffin]

Hi Rene

Shear vs peel – to be sure. But has the experiment (with a quilt) been done? It might be interesting to see just how bad the problem is. It is not as though the outer shell should be pulled away from the inner shell all that often.

Double taping – yes, extra effort. Is it easier than sewing? Don't know. It could be a whole lot faster. Experiment needed.

A question. Just what is the practical advantage of the karo design over the very conventional and much simpler linear baffle design? Is there any, apart from a very small weight-saving?

Cheers

[Adam Kilpatrick]

tape-I remember a thread where Colin Krusor (he might be watching this) showed with a diagram how he sewed baffles to a strip of cuben down the middle, then bonded the cuben. This meant the baffle pulled against tape from both sides, making it more shear rather than just peel. That increases time, if thats what you are interested in. Means no seams though, which I think there is an advantage, especially if a quilt is overstuffed so that water can bead towards the low points at the seams.

Karo advantages; if it is done just right with enough down control, means less baffle material (weight advantage), fewer seams (heat and moisture advantage). Also apparently easier to stuff as no need to weigh individual baffles out.

I think this thread is definitely thinking in terms of single digit, or maybe teen-grams (if you are lucky) Roger. But hey that's how progress is made :-)

Back to the Russian Mesh; I don't think there's any point in sacrificing weight advantages for more open baffle materials. .33 cuben baffles are pretty light, and block down between them. Especially when we are talking about minimizing baffles, making the baffles impermeable to down is probably a good idea. Of course if its lighter then that's cool too.

Roger-your quilt article is still extremely useful! Some of those diagrams make visualising things so, so much easier :-)

[Adam Kilpatrick]

At the moment I'm working on a design myself (and them MYOG) to try and get a 30 degree quilt to meet the 10oz mark without making it a vapour barrier (ie full .33oz cuben). This thread came along at a good time!

Using my current quilt (BPL 180 Long prototype) has been quite useful in working out dimensions. From this I have been able to optimise what I think will work even better-tighter in some areas eg end of footbox (where this quilt is already pretty tight at around 34-35 inches), taper it better, and give myself more width at upper torso.

When I draw up some better plans, probably over the weekend, I'll post to this thread if that's ok Rene? Some of the baffles draw on concepts from this thread, Ie angled baffles, micro baffles, etc. I've even got sewn thru verticle tube baffles in there on the outer edges! Trying hard to pick the best baffles for where is appropriate. Time to construct isn't an issue for me, I have time. I'll build up big cardboard templates for it all.

Microbaffles: difficulty in sewing these isn't too much of an issue for me, as for the few I have, I can get my Nanna to hand sew them. She is a gun quilter (of the artistic variety, not the X/SUL one) and I literally can't tell the difference by eye between a machine seam and her hand!

Actually yes, I probably own more quilts than anyone on BPL. All but the BPL180 hand made by my Nanna! I've lost count of how many she has given me :-)

[Ryan Smith]

"At the moment I'm working on a design myself (and them MYOG) to try and get a 30 degree quilt to meet the 10oz mark without making it a vapour barrier (ie full .33oz cuben)."

That will be a tall order, but I think it's an awesome goal. Don't see much pushing boundaries here anymore. I think most 30F quilts have about 8oz of down so it will take some careful planning.

I think Aaron Sorenson made a quilt(for John Abela?) a few months back where he tried to go as light as possible. Seems like he used a few tricks. Might be beneficial to find that thread.

Ryan

[Adam Kilpatrick]

Ryan, your 7D Karo quilt is a huge inspiration! I've lost of how many times I've gone back to that thread to drool over your work :-) On my side is I'm 175cm so can be shorter.

So far my ever increasingly complicated spreadsheet says YES by about 1/4 oz.

(I think google is about to start automatically pushing me to your thread Ryan as soon as I type "7" in the search bar).

[Author]

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