Design principles for the SUL quilt maker

I have made a number of quilts for summer and winter use – very successful ones.
I cannot help feeling that I strongly disagree with many of the points made above.
imho

Cheers

interesting questions.  I have thought about the same.

I’ve made a few quilts, but they’re hybrid bivy/quilt – basically, a piece of fabric goes between the edges of the quilt to eliminate drafts, pad goes inside.  So, same effect as attaching with kam snaps to the pad.

I’ve always overstuffed 30% to minimize empty spots in the baffle.  Up to 100% stuffing, down provides twice the warmth for the weight compared to synthetic like apex.  Then, overstuffing up to 150%, that down provides the same warmth as synthetic.  Richard Nisely posted about this a few years ago.

So, let’s say stuffing 100% provides a warmth of 1 unit.  If you overstuff 30%, there will be a warmth of 1.15 units.  If you made the baffle bigger to allow full lofting, the warmth would be 1.3 units.  So, by overstuffing 30%, you sacrifice 0.15 units of the 1.3 – 11.5%.  I don’t know if that makes sense.  The point is, that the overstuffed down doesn’t waste that much warmth.

If you added a middle layer of fabric, a quilt is maybe 3 yard2, lightest fabric is 0.7 osy, so a middle layer will weigh an extra 2 ounces.  My quilt has about 8 ounces of down, so, for 2 ounces, I could overstuff 30%.  But, adding a layer of fabric adds little warmth.  Adding 30% overstuff adds quite a bit of warmth, just half as much.

I agree with you that a spot in a baffle without down isn’t that bad because the fabric over it maintains an air volume which will provide most of the warmth than if it had down in it.

I have bought synthetic insulation that had a skrim layer like you describe.  It’s spun bonded with little spot welds to keep the fibers together in a sheet.  It’s polypropylene.  I’ve also bought frost protection fabric for my garden – same stuff.  It’s not very strong, easily rips.  I would hate for the baffles to rip, very hard to fix.

rsbtr has 0.5 osy bug netting.  They advertise it as good for quilt baffles.  I think that’s stronger than that skrim material.  About the same weight.  That’s probably what I would use.  I made a vest using the same material as the vest, for the baffles.  That works, but a little heavier.

I’ve tried putting non breathable fabric up the sides a little, but then I got condensation there, so now I have breathable fabric all the way down to the pad.  Under the pad can have non breathable fabric.

I think it was geoff that brought up the idea that if the quilt attaches to the pad, then there will be a volume of air next to you on the sides that is free to convect.  I think it was phd quilts that have a solution to this.  I have thought about the same thing and tried to design the quilt so it drapes down and touches you on the sides all the way down to the pad, without success.  Once I measured the temperature of that volume and it was half way between body temp, and outside temp.  I was wearing insulated vest that had about the same warmth as the quilt.  So, that tells me that air volume isn’t a problem.  If it was causing a problem, the temperature of that air volume would be less.

When the quilt is attached to the pad, there is a huge gap at my shoulders.  Once, it was very windy and not only was it cold, but sand blew into the inside of the quilt.  So, I have a triangular piece on both sides to block that gap.  Synthetic insulation inside two nylon layers.  I use synthetic insulation because I breath on it and it gets wet sometimes.

Then, I need extra insulation on my head, like a balaclava.

I do not like fabric over my face.  Yeah, it gets wet.  And it’s in general aesthetically displeasing.

Many ways to solve these problems, interesting to see what others are doing about them.

Thanks your comments Jerry, they are appreciated.  I hope I made clear I’m no expert, just having fun seeing what I can learn.

The point is, that the overstuffed down doesn’t waste that much warmth.

I’ve heard that before, and many people knowing a great deal more than I do like to overstuff, but I just don’t see what the physics is there.  Heat loss is through either conduction, convection, radiation, or evaporation, thats it.  Down conducts better than air so if there is no convection then dead air space will be better than down.  So it seems like if the loft is the same the losses when under-stuffed are mainly from the voids, which allows convection cycles to form, and from the wind washing (I’ve learned by experience how much wind washing I get on understuffed panels, its way more than I expected).  I’m both using the layer cake and the DCF on the sides to try to combat these negative effects.  It’s a subtle trade-off and experiments seem like the only way to see the answer.

I would hate for the baffles to rip, very hard to fix.

The idea of the APEX baffles is they just need to roughly stay in place.  In experiments I did they don’t rip, they just stretch since they are just stretchy strips of fuzz.  But I agree there could be longevity issues here if they shift over time.  If they start failing I’ll probably redo with some more standard baffling.. or maybe I’ll come up with some other crazy idea.

I’ve tried putting non breathable fabric up the sides a little, but then I got condensation there

Good to know, I have not done a lot of testing with the side panels yet as I just added the DCF.  I think it is far enough to the sides (there is 40″ width in the middle with no DCF, only 9″ DCF up each side) that hopefully it will be OK.  That said a bit of condensation isn’t necessarily that bad, if it stays in the quilt it is not evaporating so its a trade-off of less evaporation (loses less heat) vs more conduction through the more moist medium (loses more heat).

When the quilt is attached to the pad, there is a huge gap at my shoulders.  Once, it was very windy and not only was it cold, but sand blew into the inside of the quilt.  So, I have a triangular piece on both sides to block that gap.  Synthetic insulation inside two nylon layers.  I use synthetic insulation because I breath on it and it gets wet sometimes.

The thing over my face blocks the whole top so it’s doing a similar thing. Before I had that I had something that sounds like your triangles.

I do not like fabric over my face.  Yeah, it gets wet.  And it’s in general aesthetically displeasing.

I hated it .. until I loved it.  I don’t know what caused me to flip, maybe it was how nice it felt breathing in the warm air.  It’s definitely not for everyone and is only needed when it’s at the lower end of the temperature range.

I don’t consider myself an expert either :)

As far as overstuffed down being half as effective goes

That was what nisley measured.  I have also measured the same but my experimental setup was crude.

Here’s my explanation

With down, the fibers are very fine and don’t obstruct very much convective air currents inside the baffle.

When you overstuff, there are more fibers so they obstruct better.

Another thing is that down has less R per inch than synthetic. The down fibers are thinner than the synthetic fibers so convective currents are obstructed less.  Maybe it’s something like the loft per weight for down is 4x synthetic, the R value per inch is half, but since the loft is 4x, the R value is twice as much.

The thing is, it does not matter what the conductivity of the down fibres might be, nor does it matter what the diameter of the fibres (actually fibrils) might be, apart from a very small mass effect. The insulating power of down is due almost entirely to the boundary layer of air around each tiny fibril, and that layer can be many times the diameter of the fibrils themselves. When bits of down are packed closely together, as in a quilt, the air layers tend to merge. This means that air movement within a quilt or duvet is largely non-existent.

Yes, the loft matters, because the greater the loft, the slower the transmission of energy through the layer. The more down you put in, the bigger the loft and the better the insulation. Of course, if you try to cheat and use a lot of feathers instead of down, there will be less trapping of air, a bit more weight, and a lower cost to the mfr. But there are National Standards in many countries which limit the use of the word ‘down’. There must be no more than X% of feathers in the down.

The terms under-fill and over-fill are in themselves largely meaningless. The manufacturer of a quilt or duvet decides how much down he wants to put in (per area). That is entirely his decision. If you want a bit more, that is called ‘over-fill’, but understand that the ‘over’ word is relative only to the mfr’s standard. All the rest is marketing.

So, for example, if you are making a duvet jacket for the street, you might put in so much down, but if you are making a down suit for Everest you will put in a lot more down.

Cheers

It’s good to see such enthusiasm for making a summer down quilt, MYOG certainly needs a boost on BPL, but I believe you’re overthinking it and missing some of the basic fundamentals. Roger is right when he says that the chambers should be full. 

For quilts with less than 7 oz down fill, sewn through is actually more efficient. Might be counterintuitive, however it keeps the small amount of down in place and the chambers with enough insulation. Sure, the seams will lose a little warmth, but the plump chambers make up for it. Try baffling and you’ll get too many bare spots (with such little down). As Montbell describes their #5 Down Wrap: the use of sewn through construction allows us to keep the weight in check, while optimizing down control. HMG 40* quilt is also sewn through and rated as one of the highest warmth to weight ratios out there.

Totally agree with a 7D shell, but putting a layer in the middle? Really? Also if you can make a 20* F quilt that comes in at 11 oz and 5.5 oz fill you’ll be a millionaire overnight.

I like the chevron chamber design Loco Libre uses for their 50* sewn through Ghost Pepper quilt. https://www.locolibregear.com/product/operator-series-ghost-pepper-topquilt/#temperature-rating

I always calculate the volume of the baffle, then the weight of down to overfill by 30%.

If your baffle is 24 x 4 x 2 inches, that’s 192 in3.  900 FP down – 0.21 ounces.  30% overstuff – 0.28 ounces of down.

Then your baffles are all filled the same.

As Scott points out, the down that’s overfilled is less effective so the warmth per weight is less.

And if you underfill, there will be empty places.  What I have experienced is the baffle collapses so the two sides of fabric are touching each other – loft is about zero.  But if there are just a few places, it averages out and it doesn’t make that much difference.  It’s aesthetically displeasing though.

If you just eyeball it, you can put too much or too little down.  So your overall warmth for the weight is a little less.

I agree with another of your ideas.

On the top half of my quilt, over the torso, I have 4 inch baffles with 2 inch loft.

On the bottom half, over my legs, I have 3 inch baffles with 1.5 inch loft.

I think it’s more effective to have more insulation over my torso.  There’s more surface area.  The skin temperature of my torso is a little higher so it emits more watts.  I tend to pull up my legs a little, the fetal position, so there’s even less surface area under the bottom half.

All of the ideas considered might save a couple ounces of weight.  I would never notice that reduction in pack weight, but if I can save a couple ounces here, a couple ounces there, eventually I can get noticeable weight savings.

Thanks for all the comments.  I think the design I have doesn’t really fit the standard terms so it’s hard to use them on it.  There are no “chambers” with fixed volumes.  The “baffles” are only attached every 4″ or so in spots to the shell, and I could probably get a loft twice what I have with the same “baffles” since they are so stretchy.  So it’s almost better to just think of it as a big bag of down (with x/y but very minor z barriers to keep the down from flowing too much).

The term “under-stuffed” also doesn’t really apply as there is no fixed chamber size.  Again think of the big bag of down ideal: you could stuff it until it’s almost a spherical shape, many feet thick.  I use the term because there is less down per unit area of quilt and that aligns with under/over stuffing terminology.  For the mummy part over my body (roughly a square meter in area) I have roughly half the mass of down compared to my EE.  I have 4oz and the EE I estimate to have something like 7oz.  Then on the sides I have more like a fourth of the EE.  So I think the right term to use is weight of down per area, which Google tells me is called “areal density”.  So cross out all the under-stuffed in what I wrote and put in under-areal-dense.

The reason why I think the design does so well is I have 4″ of actual loft vs 2.5″ on my EE 20F quilt over my body.  This is a 60% increase which is huge.  I’m not sure why it’s so high when I have only half the areal density, but it has to be some combination of the extra layer of ripstop and the lack of tension on the shell.  Whatever is going on having 60% more loft seems more than enough plus to balance out the minus of under-areal-density.  I found some studies measuring what more fill would do, and in one for example 40% more fill gave less than 10% more R value.  So, yes increasing fill weight adds warmth but you are not getting the best deal for the weight added.  I have done a few A/B comparisons where I switch back and forth between the two quilts and they seem pretty similar in terms of warmth.  The main problem with my quilt was the side leakage which is why I recently added the DCF.

.. Looking over the remarks above I see I missed a couple things..

Monte said

Totally agree with a 7D shell, but putting a layer in the middle? Really?

I covered this in the original post above to some degree, but I think this middle sheet is really helping me get to the 4″ loft by riding over voids due to underfill.  As long as the voids are not too big you don’t pay a big penalty for it.  The top of the quilt is not perfectly even due to the voids, but its more slight dips as opposed to big drops; the drops would probably be a lot bigger without the extra layer since the voids would be bigger. If it really is a key component of this extra loft it’s worth it. It would be good to try a similar design without the extra layer though to do a head-to-head.

Also if you can make a 20* F quilt that comes in at 11 oz and 5.5 oz fill you’ll be a millionaire overnight.

I think the problem with the design is it’s very much a finicky beast.  It really does act like a bag of down, not like the blanket you expect.  When getting into it there is little connection between the shell layers so it moves around.  If you slept on a waterbed in the 70’s you know what I mean, before they had baffles in the waterbeds they were just a big bag of sloshing water.  Also the way it doesn’t look uniform is not something people want to buy into, even if it works.  There could also be issues with longevity.

some people swear by Caro baffles.  Where the down can move all over.  You can move more down to where it’s needed if cold, or move it out of the way if it’s warm.

That sounds similar to yours

For me, the ultimate quilt is more along these lines (Pete’s 2018 post):

https://backpackinglight.com/forums/topic/10oz-cuben-fiber-quilt/

“5# Pete‘s” design…The taped (not sewn) seams and it’s waterproof/vbl  features are impressive.    Most people probably don’t want this, but for me it would be a bonus…and without any added weight.

YMMV

some people swear by Caro baffles.  Where the down can move all over.

I wasn’t after something like that but I ended up with it.  I was thinking the baffles were going to block enough to not have any migration at all, but they didn’t.  Fortunately it’s pretty easy to even it out again with a quick shake.

For me, the ultimate quilt is more along these lines (Pete’s 2018 post)

Wow, cool stuff!  I never heard of using DCF in a quilt before so I thought it was my own idea, but apparently it’s old news.  I agree with some of the posters that mention how it’s going to produce condensation.  Generally I think today’s 7D ripstop will be better for that reason.  I did some tests with a completely waterproof cover and it’s a little too clammy in the morning for me.  Not horrible though.

The 5# Pete design is the same width that I started with (45″), but I found it too hard to sleep with such a narrow quilt.  My original was 8.5oz but I had to add 6″ to either side to make it comfortable.   I also use some non-sewn seams, glue not tape though.

I should read through all the old posts here, I bump into some good ones every now and then but clearly there’s a ton I’ve never bumped in to.

. World’s Lightest Backpacking Quilt – On The Trail – Episode #2 . Steve Evan’s video from 16 years ago, he also posted in the thread that Steve M linked.

I see it was linked in Steve M’s link, but I will leave mine anyway.

Yes I did see that one but didn’t look too closely.  It’s an interesting design with the breathable panel down the middle and the clip around the back.  It’s more for 40-50F lows though, I think he said 1.25″ loft.  Also it’s pure back-sleeper only since it conforms to your body and has no back.   In general these old super-light DCF quilts seem to not be aiming for as cold as I am trying to go.

I’m now wondering how high up the sides the DCF can run without any drawbacks on breathability.  Right now it’s only 9″ per side on mine but maybe I could go as high as doubling that.  One reason why I did only 9″ is I didn’t want to rebuild the whole quilt so I just added the DCF on top of the shell.  It added .5oz to the design which doesn’t need to be there since there are two layers of fabric right on top of each other now.  Doubling that would have meant a whole ounce more.

I’ve done some testing with the IR gun and on the torso I am getting similar numbers as on the EE 20F: my body outside clothes is averaging 85F and the top of the quilt is around 75F (this is with air temps at 25F).  The head and shoulders are warmer due to the sheet I have over my face.  The main weakness now is the feet, they are colder.  Below 40F I have been putting the feet-in-footbox into my backpack liner bag to keep my feet warm enough.  There is only one layer of insulation on the bottom end and no DCF to stop wind washing so it makes sense that they would be colder.  I’m tempted to replace the bottom panel with DCF and while the thing is apart to put a bit more insulation in there.

I would just add that durability is also an important consideration for me, and I have generally found that it becomes increasingly difficult to distribute the down in “under-filled” quilts after multiple uses (where the quilt is compressed between uses). I often read that you just need to give the quilt a shake to redistribute the down, but I don’t find it to be that simple after a few dozen nights.

I wanted to follow up on some more experiments with my quilt above.  I tested it in temps ranging from 6F to 35F.

The main place it was cold was in the feet.  I don’t like sleeping with socks and that makes things worse.  I decided to make some AD/10D booties (.5 oz each) which are loose enough that they don’t bother my feet.  With these booties my feet were toasty at 25F.  But at 15F they were again getting chilly.  So, I decided to add a bit more insulation to the top side of the footbox.  For simplicity I just put a piece of DCF on top of the existing footbox stuffed with a very small amount of down.  The DCF is somewhat stiff so it makes something like a “hat” shape over the feet with plenty of dead air space.  It was .12oz of DCF with .1oz of down in it.  I used DCF to prevent wind washing; it is a small enough area that there is still enough air circulation to keep the feet dry.

With the above setup I was comfortable down to 6F which is the coldest it got in my testing.  The main place I noticed the cold was from the pad, I was using a Tensor all-season.  At around freezing my IR gun showed 95F on the pad where my torso center was, but at 6F it was 80-85F.  Also my arms were a touch cool due to the relative lack of side insulation.

Overall I am very happy with this quilt, it started as a summer quilt but is looking more like a three-season quilt now.  The current total weight is 11.0oz.  I think the main question left is how it will hold up in the field with continued compressing and decompressing.  Even if it degrades some I still think it will be a “good deal” for the weight.  Real field testing is needed though, I’m just sleeping in my backyard now.

In retrospect I think the key to the design’s success is minimal shell tension which allows the down to loft much higher than it otherwise would.  It’s not a quilted quilt, it’s just a bag of down.  The differential fill, side closure, head covering sheet, and use of DCF are also helping.

For the record I am sleeping with shirt (3.3oz) and underwear (1.4oz), an AD60 hoody (3.4oz), an AD hat (.4oz), Montbell Thermawrap hiking pants (7.7oz) and my booties mentioned above (1.0 oz).  I was testing inside a Durston X-Dome 1+ with mesh inner.

If you add insulation most anywhere, for example the torso, then you’ll be warmer so more blood will be available to keep your feet warmer.

My feet were cold, I used booties which helped, then I got a warmer quilt, then I no longer needed the booties.

Booties are so small they don’t weigh much so maybe the warmth per weight is larger which is good

Either solution is good

I think that most of my heat loss on the torso is through the pad.  The layers are much denser and wetter below than above, so conduction will be many times more downward.  At 6F with my IR gun the quilt inside above my torso is 70-75F which is colder than the 80-85F below, but the body feel is clearly a chill from below not above, due to this wet plus compression.  So, more insulation on the torso would help, but not much is my guess.

If I was camping in 0F temps I’d get myself a Tensor Extreme or add a CCF.  With that it would then be worthwhile to also add some more quilt insulation in the core.