Feeling Down

I've just come back from Warsaw, Poland, where I have been working at a manufacturer who specializes in Down equipment. Day in day out I've been travelling to work and back wearing a variety of down jackets and body warmers. Temperatures there were usually around minus 3 degrees in the morning, but I experienced minus 7 with a fair bit of wind chill ontop.

This has been an excellent opportunity to gain greater understanding of the properties of down and the design and construction of down garments. Not least because my attention hasn't been consumed by my surroundings e.g. shaded valleys and snowy high peaks, where I've previously used down clothing (this is what I call the dog-walker effect*).

Notably, what down lacks over other insulation systems (at least, in its human utilisised form) is a system of shape regulation – it conforms to the effects of gravity and it undergoes “fibre migration”. This is why down-proof fabrics, stitch-through quilting and “boxwall” type garment construction has been developed.

What was most noticeable on all jackets was the other ways (apart from gravity) which cause down to relocate and or congregate. Here I will talk about the largest of these factors: compression & “pump”.

Compression

The armpits and the insides of elbows are both significant spots where body heat is lost. And by an unfortunate coincidence both these areas are also the insides of joints. Even the jentle swinging of the arms while walking eventually relocates down around the medial and latteral sides. The posterior elbow point is fairly thin (often with the bony end pressing the outer and inner fabrics together) while the anterior inside of the joint is completely down-free. Under the armpit the top and sides of the shoulder collect down squeezed out by the compression and passing movement of the arms.

Pump

If we do prevent down relocating in these areas, we may encounter another problem. Where down is compressed, but doesn't relocate, a natural pump is formed. The relative air impermeability of the dense woven fabric and the lofting/expanding power of the down creates a slow but strong suction that draws air in and when compressed again blows it out again. If this is just air redistributed around the inside of the clothing there isn't a problem, but if it is being drawn in and out of seams and through the outer fabric, then the wearer will have body-warmed air being steadily replaced by cold outside air as they move.

* Thanks to Charles Ross for this idea. I'll feature it in a future post. Charles, please remind me who you attributed the dog-walker comment to?