Mummy Bag Construction

Recently finished this up for someone.  Mummy bags are a decent bit more complicated than a quilt, but most of the difficulty is conceptual and in the planning rather than the construction itself. DSCF0376

For big projects, I like a couple pieces of hardboard layed out for cutting.  Dirt cheap, and easy to clean up and put away when you’re done.  A differential cut might seem scary, but is not particularly difficult.  For this bag, the shell width was about 2.5″ wider on each side as well as at the bottom.  Keep the hood area the same as the liner.

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Main body pieces cut out…

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A pretty easy way of dealing with the differential cut is putting small folds in the baffle on the liner side at regular intervals.  In this case, I had 5″ of extra baffle length to deal with.   ~1/4″ folds are easy to deal with and take up 1/2″ of baffle fabric.  Exact precision here isn’t necessary…I did a bit more than 1/4″ at each mark along the baffle plus the center seam and edges.

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I do a single draft tube/collar that starts several inches below the zipper and goes all the way around the hood.  It’s sewn on before any baffles a couple inches in from the edge to prevent any cold spots.

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I know there are less messy ways out there to stuff, but I’m pretty happy with two different cardboard tubes (bigger one to stuff down into, smaller to push it out), a tall box, and plastic bin.

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Keys to success…

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I did two sewn-through baffles for the hood on this bag.  I’ve done real baffles here in the past, but it complicates things quite a bit to have baffles running two different directions and it probably makes little difference on bags used above 0*F.  I didn’t get a photo of the pre-sewn hood, but 3d hood shape is achieved by a couple inches cut out along the baffle lines and making the top hood curve (at the point it attaches to the main body) more gradual that the curve at the top of the main body.  In other words, if they were parts of circles, the hood circle would be larger than the main body circle.

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Open to show draft tube…

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Fabric is 20d ripstop shell/taffeta liner from OWFINC and down is 850+ FP from Wilderness Logics.  Fill weight is just under 17 oz.  Bag is for a small woman; dimensions are approximately 64″ long; 54/48/36; final weight is 26.9 oz.  Feel free to ask any questions…

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10 thoughts on “Mummy Bag Construction

  1. Thank you for posting these very nice directions. Two years ago I bought the materials to make a quilt but have been unable to get past the paper work phase of construction–afraid to commit. You have given me some ideas regarding the handling of the differential cut and draft tube. Maybe I can finally get started!
    How did you handle the footbox? Is it flat, albeit that it has differential cut or did you make a separate “pillow” to attach to the bottom?
    Thanks again!

    • John,
      For a quilt, I’m a believer that a differential cut isn’t completely necessary. It may helpful in a 20 or below quilt (and then a quilt might not be what you want anyway), but the dynamic girth means that you are far less likely to completely compress the down. That said, getting everything to line up on a quilt is easier than on a bag that closes all the way, so it’s not that much more difficult to add it.

      The footbox is trapezoid shaped with a single baffle in the middle. General footbox steps:

      Turn the bag inside out and do the shell first. I make sure that the footbox piece is slightly smaller that the shell width. Make a mark at the middle top and bottom of the footbox and the main bag shell.

      Line up your marks and start sewing there. Stop a couple inches from the middle baffle line/side seams of the main bag. Now start at the bottom middle and sew up towards the side seam and again stop a bit short. This allows you to adjust the side seam stitch so it perfectly matches up with the footbox size.

      Repeat for the other side.

      If you’re a really precise measurer and maintainer of seam allowances, all this isn’t necessary, but it makes lining things up easy.

      For the liner, you can’t do it entirely inside out, because of the baffle, but you can get most of the way. Alternatively, just do the liner right side out by folding in the seam allowances and topstitch it, making sure to leave some unsewn until you stuff the down.

    • Ben, material sources/prices are linked to above. I used about 16.5 oz of down and 2.5 yards each of the .9oz taffeta (black liner) and blue ripstop (shell) from OWFINC, plus a #5 zipper, plastic snaps from Kamsnaps, and other small stuff I already had on hand. As far as time, it’s really hard to say because I worked on it over a couple weeks a bit at a time. The sewing went fairly quick (mostly done over a weekend), but the prep/cutting/etc took more hours than it should have had I taken better (=any) notes from the previous ones I’d made.

      • I see on OWFINC that there are a few choices of taffeta. The .9 oz taffeta you used is much more expensive than the others on offer. Why did you choose to use that taffeta versus the others?

  2. The others are too heavy and I don’t know that they’re calendered/downproof, plus I had the .9oz on hand and know it’s nice stuff. The cheapest option is probably ripstop 2nds from backwoodsdaydreamer.com. The 20d taffeta from OWFINC is also pretty much the same thing as M90T from thru-hiker.com which looks like it’s a bit cheaper these days.

  3. Great project! Couple of questions if you don’t mind…

    Am I correct that you cut the draft tube separately and then attached it to the lining at the seam line? Did you keep the seam allowance for both the lining and the draft tube lined up and keep that excess in the seam with the outer shell? I was thinking about cutting the lining piece a few inches too wide on one side and the top edge and folding that over for a draft tube. I cannot tell from the pics what method you used!

    How do you draft your hood for a comfortable shape? Is this based on experience?

    I’m making up plans to make a mummy bag myself and these have been mysteries to me. Thanks!

    • Hey Sarah,
      Yes, the draft tube is a separate piece. I considered making the liner piece wider like you mentioned but I can’t remember why I decided not to do it that way. I think it might have been tricky with the zipper or because the draft tube doesn’t go the whole length of the bag.

      As for the hood, I just guessed. As long as it’s big enough and has a drawstring I don’t think the shape matters too much.

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