Quilt / Sleeping Bag -- Differential Cut?

[Orion]

Unless it's only used as a flat blanket, ideally a quilt (and especially a sleeping bag) should be constructed with the inner and outer fabric cut to different sizes. But how much of a difference does it make in practice with a quilt or bag rated to ~0°C where the single layer loft is 5 cm or less? It seems that most "recipes" for making baffled quilts just go with a two-dimensional pattern. But if you wrap a quilt tightly around yourself it seems to me that this would compress the insulation between the two (same sized) layers of fabric.

Have any of you bothered with differential cut on a MYOG quilt or bag?

[Bluegum Mic]

I have only done so on two underquilts I've made for my hammock (where the differential cut is important). Id love to have a go at a down top quilt and I think I would use a differential cut. I agree it would compress less and fit around you better. Mind you if you had the quilt out flat in warmer weather it might create a gap at the foot end. Perhaps having a greater differential cut at the head end and little to none at the foot end? Now all I have to 'pluck' up the courage to handle the down

[forest]

I'm up to a sad tally of 5 "sets" of quilts, yep that's 10 quilts....(But I only have 2 sets)

UQ are nearly a must to be diff cut.

All my TQ's have been flat cuts and I havn't noticed any loss of loft when they are sealed up around me tight.

[andrewa]

I've made lots of down stuff, including differentially cut sleeping bags and jackets. Differential cuts made the whole process miles harder. For use in Oz, I don't think it's worth the fluffing around

My current sleeping quilt for snow camping in Oz is a flat baffled quilt eith 600g of 550 -600 loft local down. I do use ~8 cm mesh baffles though- they seem to stretch enough. I do sleep in fullclothing with insulted jkt and pants though, and haven't been cold yet.

A

[Orion]

Bluegum - What do you mean by "a gap at the foot end"? I was envisioning a quilt that had a permanently closed footbox area -- that's the way I use my down sleeping bag unless it's really cold: zipped up only 1/4 of the way from the foot.

For differentially cut designs, assuming the baffles run around the bag as opposed to lengthwise, don't the baffles themselves need to be cut on a curve?

Maybe differential cut will add a lot of difficulty, but high loft down and lightweight fabrics are quite expensive and I want to maximize the warmth/weight ratio. That's the point for me: to save some weight over my current sleeping bag without ending up cold at night. So the question is whether I'd notice the difference.

[Macca81]

Karo step. Easy to make differential and easier to stuff with down

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[Bluegum Mic]

Sorry Orion. I shouldn't write posts early in the morning (I never make sense that time of day lol). I meant if you had an unstitched footbox and you had the quilt open flat. If there were a diff cut it may sit up a little at the feet. But if a sewn footbox its all good

[Orion]

Sorry Orion. I shouldn't write posts early in the morning (I never make sense that time of day lol). I meant if you had an unstitched footbox and you had the quilt open flat. If there were a diff cut it may sit up a little at the feet. But if a sewn footbox its all good

Early morning posting aside, how could you have known what I had in mind? But I get what you're saying now. If it's made to be curved it won't sit flat as well. I'm having trouble picturing what will happen and was hoping to avoid sewing mockups, but maybe I'll have to do that.

When you made your underquilts did you cut the baffles on a curve? Or did you run the baffles lengthwise?

[Macca81]

Not sure what full length baffles would be like for a differential cut, but my UQ sits flat when laying flat and still lofts fine when under my hammock...

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[Bluegum Mic]

Unfortunately both the underquilts I made were synthetic and didn't require baffles so Im no help. One was climashield apex, the other insultex. So the more I think about it, Macca is right in his above post. The reason I was envisiaging the foot end gap (if a quilt had a snap closure foot box and could be opened out flat) is because the synthetic fabrics stand up a bit more rigid (both the synthetic ones I made certainly curved when on the floor where I don't notice it with my down underquilt). If down it would drape better so I don't think it would be an issue. Seeing as your sewing the footbox its all good anyway

I was reading a really good DIY design of a top quilt the other week and it was differential cut from memory. Ill see if I can find the link and what baffles they used.

You'll definitely have to keep us posted with which way you go as its definitely a DIY project I've wanted to do for ages.

[Macca81]

Slightly off topic, looking at making a summer UQ, and looking at synthetic just for something different. Do you have any opinions on the differences between climashield and IX? In terms of working with them and performance?

[Orion]

Bluegum, if you can find that link I'd love to see it.

I can understand how a flat sewn quilt, if loosely wrapped, will have wrinkled extra inner fabric (and baffles) and the loft shouldn't be affected. But if the quilt is wrapped tightly around you a flat cut will result in compressed insulation. Maybe it only happens at sharp inflection points and so isn't as bad as I'm imagining.

If the quilt is differentially cut but the baffles are flat a tightly wrapped quilt will compress the insulation near the baffles but not in between them. I can visualize this but not perfectly. And I can't figure out how much it will matter. It's tempting to just sew the whole thing flat as that's so much easier. But the materials are expensive.

Excuse me for putting it this way but I'm somewhat "baffled" about how best to proceed.

[Macca81]

If the quilt is differentially cut but the baffles are flat a tightly wrapped quilt will compress the insulation near the baffles but not in between them. I can visualize this but not perfectly. And I can't figure out how much it will matter. It's tempting to just sew the whole thing flat as that's so much easier. But the materials are expensive.

I don't know if you have considered going down the Karo step path, but it makes sewing differentially fairly easy, and still being able to sew flat. Use a pattern for where the baffles go on the inner, then just increase the pattern size for the outer. Baffles are all just rectangular pieces and it's the gaps between the baffles on 2 axis' that makes it all work flat or curved.

If you want, I'll try and dig up the pattern i used and take a pic to give an idea on what I'm trying to say :p


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[Orion]

I don't know if you have considered going down the Karo step path, but it makes sewing differentially fairly easy, and still being able to sew flat. Use a pattern for where the baffles go on the inner, then just increase the pattern size for the outer. Baffles are all just rectangular pieces and it's the gaps between the baffles on 2 axis' that makes it all work flat or curved.

If you want, I'll try and dig up the pattern i used and take a pic to give an idea on what I'm trying to say :p

No, I wasn't even sure if your original suggestion was serious or a joke. All those individual baffle pieces and then stuffing so many boxes with down didn't sound like what I wanted to do. But I appreciate the advice and the offer of a pattern. It's too late in any case as the design decision has been made, the fabric has been cut, and the sewing (sloppy as I am with it) has commenced.

[Bluegum Mic]

Well done Orion. I posted the other day but the post didn't work (tapatalk does weird things sometimes). What I did post was I hadn't found the link but Im still looking. I was googling something strange at the time and can't for the life of me remember what it was . Im designing a pack atm that I want to make and it may have been to do with fabrics but??? Sorry.

Did you go with a differential cut in the end? Can't wait to see the pics:smile:

[Macca81]

Stuffing individual boxes? No, just one giant box! I went the way I did to avoid having to stuff multiple baffle tubes! Weigh out the total amount of down needed for the entire quilt, then stuff it all at once.

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[Orion]

Well done Orion. I posted the other day but the post didn't work (tapatalk does weird things sometimes). What I did post was I hadn't found the link but Im still looking. I was googling something strange at the time and can't for the life of me remember what it was . Im designing a pack atm that I want to make and it may have been to do with fabrics but??? Sorry.

Did you go with a differential cut in the end? Can't wait to see the pics:smile:

I spent time measuring and examining my Western Mountaineering bag. I got into it normally and with it turned inside out; I stuffed it with a big duffle bag both normally and inside out as well. What I found was that the differential cut was relatively small for this bag. When inside out the loft seemed a little less, but only slightly. There was also noticible extra material bagging up inside when the bag was inside out. But I wasn't sure exactly how much or where the optimal differential cut should be. It's an interesting problem.

So I ended up cutting the inner fabric 5 cm narrower in width, from top to bottom. It's such a small amount I'm not sure how much difference, if any, it will make. Rather than shape the baffles I just added darts. I'm such a lousy tailor, so sloppy, that this tiny refinement is riciculous given how inaccurate everything else is. If you look closely you will suspect that I sewed it while very drunk. But hopefully it will still keep me warm.

I inhaled a down feather just a little while ago.

[Orion]

Stuffing individual boxes? No, just one giant box! I went the way I did to avoid having to stuff multiple baffle tubes! Weigh out the total amount of down needed for the entire quilt, then stuff it all at once.

So Karo step implies open baffles? Both horizontally and vertically?

I'm intrigued, but it's too late to explore the possibility. And it's very unlikely that I will ever do this exercise again.

[Macca81]

So Karo step implies open baffles? Both horizontally and vertically?

I'm intrigued, but it's too late to explore the possibility. And it's very unlikely that I will ever do this exercise again.

Spot on. The down is free to be shifted to any point you want, while the baffles still prevent it from migrating on its own. It is this vertical and horizontal open sections that allow it to be curved in any direction or laid flat while maintaining loft. The fact that it curves up in all directions from my bum in the hammock was the very reason I went with this design.


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[Orion]

Spot on. The down is free to be shifted to any point you want, while the baffles still prevent it from migrating on its own. It is this vertical and horizontal open sections that allow it to be curved in any direction or laid flat while maintaining loft. The fact that it curves up in all directions from my bum in the hammock was the very reason I went with this design.

Is this a typical baffle pattern for what you're talking about?



I took this from a youtube video where a guy made a quilt out of Cuben and down. He says in the video that the whole point of Karo step is to make the process of stuffing the down easier. He then goes on to show himself (in fast motion) stuffing and stuffing and stuffing (feathers stuck to his arm and floating in the air) and stuffing and stuffing and stuffing... It didn't look all that easy!

His comment made me wonder -- Is Karo step just a method for easing construction? Or does it have advantages in the finished quilt/bag? To put it another way, why are high quality sleeping bags made with horizontal baffles instead of Karo step?

[Orion]

So it turned out okay despite my worries over really slippery fabric and sloppy stitching. Stuffing it was actually the easiest part.





It has about 340g of 900 fill down and a total weight of 528g. I was aiming for a little over 180cm long but every time I sewed anything it shrank. As it is it reaches my chin just fine. I sewed it up about 65cm from the foot, pretty much how I like my bag when using it in quilt mode. I also added a little snap at the top so it will stay around my neck. I'm not sure if it needs straps; I hope not because I'm not adding them.


Now I'll go and see how it works!

[Bluegum Mic]

Looks fantastic Orion. It turned out really well. What method did you use for dividing up the down for each baffle. Im an ok sewer...its the working with the down part that keeps turning me off this project (especially as Im allergic to it...there'd be a whole lotta sneezing and antihistamines for this project

[Orion]

I used the vacuum cleaner method. I found a cardboard tube (the kind gift wrapping comes on) and it fit right onto the vacuum cleaner nozzle, which I wrapped with noseeum netting. The vacuum cleaner sort of struggled when the tube started filling with down so I had to reach into the bag and stuff it to help it along. I suppose a shop vac would be better but ours is really noisy.

I could get about 15g of down in the tube. Then I'd insert it deep into a baffled compartment and push out the down with a broom handle. This would leave a very compressed block of down far from the entrance. So it was easy enough to pull out the cardboard tube, load it up, and repeat. Once filled I'd tape the end shut just to keep random feathers from escaping. I had to do two fills for each of the 14 compartments, plus several more for the two compartments in the footbox end. I thought filling would be a big messy chore but it was easy and went fast. It was the sewing that was so frustrating for me. That slippery fabric; I just couldn't get anything to stay put. It was like trying to sew a jellyfish.

I measured the down by subtracting from the weight of the package full of down. Either my scale was drifting or I made some error because I was expecting to have a little down left over after the last fill and instead I used every gram.

I did this all in a small bathroom and there was a bunch of down floating around. But when all vacuumed up afterwards it didn't amount to very much, just a fraction of a gram.


It is very easy to inhale small down feathers. If I were you I'd wear a mask and gloves when doing this. But how can you even think of using a down quilt if you are allergic?

[Bluegum Mic]

With a whole lotta eye rubbing and sneezing I don't use down at home as that's just being a glutton for punishment, but when on the trail the weight to warmth ratio outweighs the sneezy factor for me. I just usually carry a few antihistamines with me. I don't usually use them as Im used to the odd sniffle but sometimes if Im having a bad time with it I will. I usually find the longer the trip, the worse I get.

Sounds like the filling was easy enough then. I really should do this project, though at the moment I must admit Im toying with a pack design that id like to make.

[wayno]

that looks absolutely fantastic. as good as any commercially made bag..
can i ask how much the materials cost and the total time?

[Orion]

Thanks, I'm pleased with it. The stitching is sloppy and puckered and funny in places, although not enough to affect either its function or its appearance from a short distance. But if you could examine it closely, trust me, you would be unwilling to pay a commercial price.

I bought the M50 kit from thru-hiker.com. I wanted the lightest materials I could afford. It was expensive but still only half the cost of the same-weight bag I would have bought (WM Summerlite). The Summerlite has 25% less down but is a mummy bag with a hood. Odds are it's warmer than my quilt but I'll never know for sure.

edit: I'm not sure how long it took as the work was sporadic and spread over about five days. I didn't keep track but if I had to take a wild guess I'd say 15 hours.

Last edited by Orion on Sat 22 Sep, 2012 4:27 am, edited 3 times in total.

[Macca81]

Looks great!

Stuffing down is only ever as messy as the method used, what you are stuffing it into has very little effect on the mess.

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[Orion]

I took it out for a long week in the California Sierra where it is the tail end of summer. It never got down to freezing where I camped. Coldest night was maybe 3 or 4°C (guessing). It performed quite nicely, sans tent. It seemed to work best if I was on my back but it was fine while side sleeping. It's just long enough to cover my ear. Switching positions took some effort and technique to avoid letting in too much cold air.

I was careless and tore a very small hole in the fabric where it's sewn together near my knees. I knew that was a stress point. A piece of tape covered the hole well enough to keep the down from escaping. I'll have to sew on some sort of fabric reinforcement for that area.

It's a summer bag. I don't think a quilt, even a bigger, loftier one, makes sense for sub-freezing conditions, at least not for me. Cold enough and I'd want a hood and zipper.


edit: I just checked the on-line temperature data (available for one place I slept) and supposedly the low that night was 0°C. I was toasty in my bag!

[forest]

Hi Orion, Looks really nice. Good work.

I was careless and tore a very small hole in the fabric where it's sewn together near my knees. I knew that was a stress point. A piece of tape covered the hole well enough to keep the down from escaping. I'll have to sew on some sort of fabric reinforcement for that area.

Bugger.
FYI here's a picture of the reinforcement area of my hammock gear TQ. Might be of help. I'm pretty sure it's a double layer of 10D. (This TQ is M50 outer, 10D inner)

IMG_4465.JPG (56.73 KiB) Viewed 69156 times

[Macca81]

My nunatak TQ has a similar triangle in it. Really helps to prevent that lateral pulling of the seam.