What is down?
Down is the fluffy plumage that waterfowl grow next to their skin to help insulate and aide buoyancy. It is not a true feather as we understand them, but a much simpler form that has soft and fluffy filament shafts growing in all directions. These down ‘clusters’ are extremely lightweight and provide a large surface area to trap air and warmth from the body. True feathers grow over the top of the down and help shield the birds from wind and water penetration, as well as aiding flight due to increased aerodynamics.
Why use goose down?
All waterfowl produce down, but geese and duck down are the most popular as it is a by-product of commercial farming practices. The most sought after down comes from adult geese as they have a very fine cluster construction, providing more loft than juvenile goose down or duck down.
One of the major advantages of down is its warmth-to-weight ratio. No synthetic insulation even comes close to matching it. So producing a like-for-like jacket, the down insulated one is going to be much lighter than the synthetic insulated one. Combined with this is the compression advantage of down. You can scrunch up down jackets in to very small shapes without damaging the clusters. If you want to wear one that has been jammed in to an awkward shape in yor backpack, just like a duvet, all you need to do is waft it a little bit to increase the loft.
Negatives of down insulation
Downs Achilles heal is moisture. If it gets too damp or is waterlogged, then the clusters stick together, drastically reducing the surface area and thus the insulation properties. Drying down takes a very long time unless you have a tumble dryer, so if it gets wet when you are outside, then it is going to stay wet and offer little protection from the cold. Fortunately, new hydrophobic treatments have started to be applied to down clusters to help repel water for longer. Using this treated down produces an insulated jacket that is not waterproof, but it will function a lot better in damp and wet weather, will dry quicker, and will retain the loft of the down even when wet.
For more information on down and its properties then please visit the EDFA European Down and Feather Association