Originally Posted by

**Schneiderlein**
The following method has worked well for me (warning: some math talk follows). For a baffled quilt, you take the loft L as the height of your baffle (and then overstuff), so you have a down area per unit length of L * W, where W is the width of each down chamber. I figured with a differentially cut quilt, you want to have the same area per unit length for insulation. So, I computed the parabola with zero crossings at -W/2 and W/2 that would give me an area under the curve of L * W. Then I took the arc length of that parabola as the chamber width for the outside. Since catenary curves are so popular around here, you could go through the same exercise with a catenary curve. It would be interesting to see how much of a difference it makes.

This approximation has worked well for me, but I split the down volume between baffle and differential cut. On a sewn through quilt, the approximation may not be as good (or it might be better), but it's a starting point. YMMV.

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