A few years ago, an engineering student aat Georgia Tech did his masters thesis on developing a model for the mechanics of compressibility of down … for the known reason that down is a highly compressible substance, and there wasn't much theoretical basis for its behavior.
The first two chapters of it are of general interest as it discusses the geometry of down and has interesting illustrations.
The theoretical development and verification of the model is of less general interest.
It can be found at:
