I only did a width differential. I took the pattern from the "hammock" part of the wooki and stretched it by 15%. Unfortunately, the down under my feet is quite compressed. Below 30°F I have to use a foam pad under my feet. Not a big issue, but not perfect. Also, the width differential could be slightly more.
Recently, I took another thorough look at the original Wooki and recognized that Brandon also did a lengthwise differential. There are two fold on the sides of the insulated area, right beneath the feet. This gives the down more space to loft there.
What I would do different:
1. 20% width differential, one fold at each chamber.
2. 3% lengthwise differential, one fold in the foot area.
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