DOWN 101: The Essential Guide to Nature’s Best Insulation
The essential guide to nature's best insulation, thermal efficiency, fill power, and field performance explained.
What Is Goose Down?
Down, as used in the outdoor industry, is the layer of fluffy plumage found beneath the outer feathers of ducks and geese. Unlike feathers, down has a three-dimensional structure with no stiff quills, only small filaments growing in all directions. It is this structure that traps air molecules in tiny pockets, creating a highly effective thermal barrier. There are approximately up to two million filaments per ounce of down, each one trapping air in these microscopic pockets.
The thermal efficiency, warmth-to-weight ratio, and compressibility of down as an insulating material has yet to be replicated by any synthetic insulation. Duck and goose down remain warmer than any known synthetic alternative at equivalent weight.
Who Invented the Down Jacket?
Australian chemist and alpinist George Finch is credited as the creator of the first down coat used as a technical outdoor garment, commissioning one for the British Everest Expedition in 1922.
Second from the left in the front row, George Finch can be seen wearing his distinct down coat in contrast to his peers in English wool tweeds and gabardines. George Mallory sits to his left.
History of the Down Jacket
The modern quilted down jacket with stitched baffles, as produced today by any number of outdoor brands, traces its origins to American outdoorsman Eddie Bauer. The distinct stitched-baffle down jacket was patented in the US by Eddie Bauer in 1940.
What Is Fill Power?
Without getting overly technical, fill power is a relative measure of the loft, or "fluffiness," of down. The higher the fill power, the more air a given weight of down can trap, and therefore the greater its insulating properties. Higher fill power means fluffier, lighter, and warmer insulation.
- 1 oz of 600 fill power down will loft to 600 cubic inches.
- 1 oz of 700 fill power down will loft to 700 cubic inches.
- 1 oz of 800 fill power down will loft to 800 cubic inches.
800 fill power is generally considered the start of the excellent range, topping out at an absolute pinnacle of 950-1000 fill power.
Duck vs. Goose Down
Performance-wise, there is no measurable difference between duck and goose down until you reach the mid-800 fill power range. Beyond that threshold, only geese produce down clusters large enough to achieve fill power ratings of 850 to 1000.
Gray vs. White Down
There is no performance difference between gray and white down, they are identical in every way except color. White down requires more sorting to isolate and is best suited to garments with lighter shell fabrics where down color might otherwise show through. It is a cosmetic consideration only.
Down Jackets and Rain
Down jackets were not designed as rain jackets, and understanding this distinction is essential to getting the most from them. The one vulnerability of down is water. When saturated, down loses its ability to trap air and with it, all of its insulating properties. A soaked down jacket offers little more warmth than a wet t-shirt, which is why knowing when and how to wear one matters.
The next generation of technical treated goose down addresses this vulnerability directly. A process is applied to coat each individual down cluster filament, making the down hydrophobic, repelling water while fully retaining its air-trapping, insulating capabilities. This treatment adds no weight, does not reduce compressibility, and keeps the down dry up to 27 times longer than untreated goose down. It is a meaningful advancement that extends the range of conditions in which a down jacket can confidently be worn.
That said, even treated down jackets are mid-layers, not waterproof shells. In sustained rain, the correct approach is to layer: down mid-layer for warmth, waterproof shell over the top. Together they cover far more conditions than either can alone.
PDW uses state-of-the-art next-generation performance goose down in our down mid-layer jackets.
Why Choose a Down Jacket?
Quality down jackets share the virtue of exceptional warmth with a featherweight feel. This class of technical mid-layer has broad appeal because in cool and cold conditions, nothing keeps you warmer with less perceived weight. In the wilderness, that translates directly to speed and freedom: go fast, go light, stay protected from the chill, and pack down small enough to stash in any bag. Originally developed for alpinists, the down jacket remains a favored technical mid-layer across a wide range of backcountry pursuits.
With today's advancements in water-repellent finishes and treatments, down jackets can be worn longer and in a wider variety of conditions while retaining their natural characteristics. That said, a down jacket is still not a rain jacket. A DWR-treated shell buys enough time to shed initial rainfall and swap to a waterproof outer layer, not to stand in a downpour.
