Making a sleeping bag, questions about karo, sizing,…

[Mark Dijkstra]

I just finished one project, now it's time to start another. My current sleeping bag sucks, so I want to make a new one. Before I begin, I do have a few questions that I'd like an answer to.

1) I already had most things figured out, but then I found out about karo designs. Karo designs are apparently easier to fill, but there are more baffles, so it takes longer to make. However, I have not been able to find anything about real (dis)advantages of a karo design compared to a "standard" box/trapesoid design. Which design is warmer/lighter/better?

2) For sizing, I figured I'd roughly copy the size of a bag that I like. When I measured the individual panels of that bag, I noticed that the bottom panels of the bag were less wide than the top panels. Why would this be done? Why not have equally large top and botom panels?

3) I want the inner fabric to be smaller than the outside fabric. That way it's more difficult to compress the down. How do you calculate how much the difference between the inner and the outer fabric should be?

[Adrian MITCHELL]

The last thing you referred to is called a differential cut. I just finished a baffled Karo quilt, with baffle heights of 2". I went with a 4" differential cut because that was what I saw on the specs of a similar quilt made by Katabatic. Hope that helps.

What kind of loft are you aiming for?

Also, in terms of which is better, a sewn through Karo quilt has about half as much stitching involved, so the cold spots are 50% smaller. there would not be a noticeable weight difference. For a baffled quilt, you save 50% of your baffle weight, so you are saving a little wight, but the performance would be about the same (no cold pots either way).

Adie

[Mark Dijkstra]

Differential cut, it was on the tip of my tongue, but I couldn't remember what it was called.

I'm aiming for about 5cm of loft, which sould keep me comfortable at or slightly below freezing temperatures. If I used a karo design, what would be a good size for the chambers?

Also, whould there be a difference between designs in their ability to stop down from falling to the side and keeping it on top of me?

[Sam Farrington]

Thought when I got to it, would just dig out the formula for the circumference of an elipse, and us it to figure the width of the inner and outer shells. It ought to be close enough.

[Jerry Adams]

"Thought when I got to it, would just dig out the formula for the circumference of an elipse"

Just use circle

Circumference is 2 * pi * radius = 6 * radius

For loft of 5 cm you want outer to be 30 cm longer

Except for quilt it's just on top so maybe 20 cm longer

[Mark Dijkstra]

Thanks, that helps a lot.

Now I only have 2 important questions left.
1) Are karo designs better at keeping down on top of me and preventing it from sliding to the sides?

2) What is a good size for the square chambers in a karo sleeping bag?

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