Assuming all other things being equal, which is a big and probably unrealistic assumption, your "fill factor" might have some use. It also assumes the down tubes are stuffed to the same degree of fullness.

Loft is still the determining factor between similar jackets, but if you can't see them in person, the "fill factor" might be an additional parameter to consider.

I miss catalogs.
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Always remember that you are absolutely unique, just like everybody else. -Margaret Mead