Down is the soft, airy layer found beneath the feathers of ducks and geese. The fluffy clusters trap air and body heat, which makes down one of the warmest fillings for its weight. It also compresses easily. That is why it is used in many winter jackets and in the classic puffer jacket.

How does down compare with feathers, and what does fill power measure?

Feathers form the bird's sturdy outer layer. Down is the soft part underneath. A filling with a lot of feathers is therefore heavier and less airy than one made of pure down. How well down insulates is shown by its fill power: this measures how much space a fixed amount of down takes up. With a high fill power, you need less down for the same warmth. The jacket is then lighter and packs down smaller.

Choosing duck down or goose down

Geese are larger birds with larger down clusters, so goose down more easily reaches a high fill power. At the same fill power, duck down and goose down insulate equally well. When choosing a jacket, look at the fill power rather than the bird.

Down or synthetic in wet weather

Down works best in dry cold, because wet down loses its insulation. A synthetic filling stays warm even when it gets damp. If you choose down, look for the Responsible Down Standard (RDS) certification: it guarantees that the down does not come from birds that were live-plucked or force-fed. Prefer no animal filling at all? Save the Duck offers jackets with Plumtech, a synthetic filling made of polyester.