Most compressible volumes: synthetic fibre versus natural eider down?

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Summary:
What materials will compress and subsequently re-expand naturally to the greatest volume? Can better materials be made? Can we yet make 'fractal' branching fibres?
I'm just purchasing some exped kit including coats and sleeping bags containing down as the insulator.

The key superlative of down is that it can be compressed and then recovers to a big volume. If one ounce of material re-expands, after compression, to 800 cubic inches then this is called '800 CUIN'. (Basically, just twice the density of air!) Commercially supplied items are variously rated 400 to 800 CUIN.

It got me wondering what is so special about down and why we can't improve on it artificially. Of course, its performance is all to do with some sort of 'fractal' branching, which nature seems good at, of ever finer hairs on a feather stem.

My question is; for any solid-structured materials compressed for a day and then allowed to expand, are there any better materials than eider down, naturally or man made? If so, what are they, and if not what are the manufacturing limitations in which the physics and engineering stop us reproducing this natural wonder?

We are good at making natural fibres, but I am guessing the inherent compressibility of down is down to the fractal branching of the feather structure, rather than the fibres that make the feather? I don't know if that is right, but if we could figure out a way to manufacture fibres in a fractal form rather than just hollow or clever cross-sections then maybe that is a way? Has anyone in the world achieved this or working towards it?

Also, in such an engineering solution it would be worth compromising on compressibility a little if it gives stiffer support to compressive loading, as down pockets compress flat with relatively little pressure. This is one of the trade-offs with synthetic fibres. I have one product which is down and synthetic fibre mixed, which seems on the face of it to be a good solution but maybe there is an undesirable interaction between the mechanical strands of each part, I will find out in due course!

Another reason for wanting to reproduce the features of down is that down works poorly once wet, whereas a hydrophobic fractal fibre could be ideal?

I am imagining these are not original thoughts, for those whose business this sort of thing is, and someone is already working on this?
 

Answers and Replies

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Baluncore
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Down was a low cost traditional material, a byproduct of food production. As clothing, it was not designed to get wet, so was used inside, or outside in cold dry conditions.

I would consider a structure made from several layers of knitted wool or hydrophobic fibre. The difference between knitting and weaving is very significant when it comes to included voids. Whatever you use, it will require a wind-proof envelope, probably close woven.
 

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