a long time ago and far far away...
I spent a summer on a 4 moth camping trip with a US mountain regular armed forces sleeping bag with a treated cotton shell and stuffed with "1/2 water fowl feathers and 1/2 chicken feathers". It was an awesome warm bag that never lost any loft, of course it was just rolled up and slung under my pack frame. Ishi wore a jacket made of bird wings.
Jim
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.