Can anybody tell me if there are documented differences in how long different fill-power downs will retain their original loft?

Based on really limited observations, I would have to say that the lower fill power downs (eg. 500-600) appear to be more durable than the more expensive, higher fill-power downs. This is based on experience with older and heavier down gear and comparing it with newer high-fill, lightweight gear.

As an example, I have a circa 1972, REI down sweater that was probably originally made with 500 to 600-fill down. As best as I can discern, this garment has lost relatively little loft in the 35 years I have owned it. I also have a circa 1956, Eddie Bauer down bag filled with feathery down that, while pretty skanky, has nearly it's original loft. Both of the older pieces of gear have had a lot of use. In contrast, I have a quilt I made using 800-fill down that seems to have noticeably lost loft over four years of gentle, careful use. The same observation applies to an 800-fill down jacket that I made.

I concede that the above is not a rigorous test of any hypothesis but it seems to be a legitimate question. Moreover, I think I could make a theoretical case that the cheaper down, while heavier, could also be more robust.

Would anybody with experience in this care to comment?
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