Sleeping bag construction

Hi Brad

As it happens … we do have an MYOG quilt/SB article in the pipeline and due for publication … soon ..

> the recent bag lost about 5 functional inches in length once I stuffed it
That's an awful lot! One or two inches I could understand, but 5? Ah well, just make the fabric that much longer and a bit wider? After all, this is one place where exactitude is probably not absolutely essential.

> My first instinct is to create a baffled bottom shell and a baffled top shell, then sew them together.
For some strange reason, most good down-proof fabric is just wide enough to let you cut the whole shell out in one piece. I really don't see a need to have two lengthwise seams. I don't.

Do you want a differential cut? That is good for a winter bag with lots of down, but sewing the baffles to the different width layers is a whole new level of difficulty! It can be done though.

Cheers

The more you over stuff the chambers, the more "shrinkage" you get.

Roger, I was thinking the same thing about most fabrics being just wide enough. But the Momentum I used in this last project was 58.5 and 59 inches; for a finished girth take off about an inch. Take off a little more more loft, and it's a functional girth in the 56-57 inch range. By comparison, many people consider a Summerlite at 59 inches to be narrow. My next project (I think) will be about a 10*F bag, I'd like to have the finished girth 60-62 inches. Does anyone make wider yardage? Other recommendations?

Michael, good point. My initial thoughts were that since I only used 6 ounces of down in my recent sleeping bag there was no way it was overfilled. But by using a slightly shorter baffle height than my target loft, each baffle has an extra half-inch of "poof." Of that would shorten the bag a bit more. Can't believe I didn't think of that. Thanks!

Edit: Just thinking about cutting the shell from one piece of fabric… My basic concern is that I don't understand how you could cut a complex curved shape from a single piece you basically expect to fold over. In other words, how could you get the shape of something like a WM Summerlite by cutting the shell out of one piece of fabric and folding it over? It doesn't seem like that's something you could do.

Hi Brad

Yeah, 59" is pushing it a bit. But maybe the people who *normally* use Momentum make narrow bags to minimise the weight? (Not necessarily a good idea.)

Now, how to get a complex curved shape? Well, it is an interesting exercise to compare the shell weight for one of those bags with curved sides against the shell weight for a bag with straight/tapered sides (and one folded side). I will bet that the difference is way down in the region of 10 grams.

Even if it is more than that, you have to factor in the weight of the *extra* fabric required for the extra seams needed. This is actually not insignificant!

And I HATE those bags which jam my knees together!

So why do big companies make sleeping bags with these curved shapes? For several reasons:
1) They look very technical, even if they aren't
2) The cost of the sewing labour in China is next to zero
3) Marketing designed the bags with Photoshop rather than advice from experienced walkers
4) Marketing think it gives them a competitive advantage

By the way – don't laugh at 3). This IS how many day packs and even larger ones get designed by some companies today. Packs are being designed by graphics artists for *looks* rather than by experienced users for function. Insider info.

Cheers

I've recently made a sleeping bag and I'm pretty happy with it. What I really like about my gear is that it has exactly the features I want and is tailored exactly to fit me. You won't find such a bag in a shop. Here is what I learned:

Firstly, make full size model from some cheap material (I used painter's plastic) to try how it fits. I used another sleeping back inside it to simulate the thickness of the insulation. The best way is to start with a large pattern, you can easily trim it where needed in the process.

I found a 'shaped' pattern more comfortable than a straight tapered one, although it might not be exactly a shape used to cut down all unnecessary weight. The curved pattern allowed me to maintain reasonable circumference around my hips without being unnecessary wide at shoulders. I found this dimension quite important to be able to huddle up with the bag without compressing the insulation or stretch my arms along my body. Aside the aesthetics, rectangular torso part with the rest tapered will work the same.

I used momentum for it, and it was not wide enough to make the from one piece, even though the bag is relatively narrow (somewhere between the minimalist style and mainstream comfort), so it was necessary to make it from two pieces.

Regarding the length, I think I've lost not more than 5 cm (2") after the filling. I planned for something like that, so it ended up well. It's a summer bag, definitely not overstuffed.

Overall, I used a design similar to Roger's – 3/4 length zipper in the middle, so that the bag can be used as a very comfortable quilt.

Hmmm. Thanks, guys.

I do mock things up in plastic or cheap fabric first (old bedsheet, anyone?). I think the reason for my interest in a design with more complex curves is two-fold. First, my straight-edged design doesn't seem to give me the same kind of fit options as curves would. Specifically, to get the taper I want around the hips the chest ends up more tapered as well. Secondly, I've noticed that there is some bunching and gathering of material along the center zip of my bag. Playing with the material a bit, there is an significant and obvious pucker at the point where I cut the taper in from the widest point of the bag. In other words, if you were to fold the quilt-style shape onto itself, one edge will be totally straight, the other will have the tapers cut into it. When you sew a zipper into that tapered edge you get an odd pucker that doesn't seem to contribute significantly to overall girth. My guess is that by cutting a shaped bag I should easily be able to ditch the pucker and maximize girth: fabric usage and fit. Guess we'll see. Have to wait a while before the budget can take another hit on down and fabric.

Guys,
One option if you want to make a bag that is wider than the width of your fabric is to NOT cut the fabric with the "pattern" running lengthwise down your roll of fabric. Instead, you could design the bag with one seam that runs perpendicular to the normal length of a bag. You could cut a "head end" of your bag as wide as you want, and attach it to a "foot end", also as wide as you want. In this orientation, the maximum length of the bag is now twice the width of the fabric. The seam would be easy to sew, and if you placed it at a baffle stitch line, it would blend right in. A great book on making your own stuff is by Gerry Cunninham: "Lightweight Camping Equipment and How to Make it". (1976, but a library may have it) I will also take a fabric measuring tape to a sleeping bag that seems the right size. You can stretch the fabric to measure the girth every few inches and do some reverse engineering. I also will gently tug on baffle seams to determine where they attach. You can learn a lot about how things are made, without ripping a seam. Look especially around the draft tubes, side block baffles, and the hood and foot sections. Scott