How to Wash a Down Jacket

The Chemistry

Down is the soft underlayer of waterfowl plumage — the clusters of fine, fluffy filaments that lie beneath the outer contour feathers of geese and ducks. Each down cluster consists of a central quill point with filaments (plumes) radiating outward in three dimensions. Each filament in turn has tiny sub-branches (barbules) that interlock loosely with adjacent barbules on neighbouring filaments. The result is a three-dimensional structure that traps enormous quantities of air relative to the cluster's own mass. The key measurement of down quality is fill power — the number of cubic inches that one ounce of down occupies under a standard laboratory weight. 800-fill down occupies 800 cubic inches per ounce; 550-fill occupies 550. Higher fill power means more trapped air per unit weight, which means warmer insulation for the same jacket weight. The trapped air is what provides the thermal insulation — down itself is only marginally insulating; the dead air space within the barbule structure is the insulation mechanism. This explains down's catastrophic performance when wet, and why washing must be done correctly. When water contacts a dry down cluster, the water molecules are attracted to each other (high surface tension of water) and to the polar groups on the keratin protein surface of the barbules. As water penetrates the cluster, capillary action draws water into the spaces between barbules. The surface tension of the water films between adjacent barbules creates a net attractive force — the barbules are pulled toward each other. The three-dimensional cluster collapses into a matted, flat lump. The trapped air is expelled. Fill power drops from 700–900 to near zero. A wet down jacket provides almost no thermal insulation. There are two equally important steps to restoring loft after washing: drying and re-lofting. Drying: all the water must be evaporated from within the clusters. This takes much longer than the outside of the garment feels dry — the clusters deep within baffles can retain trapped moisture for hours. Tumble drying at low heat for 2–3 hours is the correct method. Air drying leaves persistent moisture in the innermost clusters and can cause mildew to develop on the down. Re-lofting: even when completely dry, collapsed down barbules that were compressed together by surface tension will remain stuck together unless mechanically separated. The water has evaporated, but the barbules are now in direct contact, held by van der Waals forces and possibly by residual substances (natural oils, detergent film). The clusters need to be physically agitated to re-separate the barbules and allow them to spring back to their three-dimensional configuration. This is the function of dryer balls: clean tennis balls, wool dryer balls, or specially designed laundry balls tumble with the jacket and periodically impact the clumped down, breaking the barbules apart. Without dryer balls (or repeated manual shaking and fluffing), washed down dries into a hard, lumpy mass with almost no loft — effectively destroying the jacket's insulation even though the garment is technically clean and dry. Regular laundry detergent presents an additional problem. Down's barbules are coated with natural keratin proteins that have an associated oil coating (from the bird's preening oil, distributed across the plumage during grooming). This oil coating allows the barbules to slide against each other smoothly as they re-expand during loft recovery. Regular laundry detergent (particularly standard surfactant-based detergents) is effective at emulsifying and removing oils — which is exactly what you want on a cotton shirt collar, but not on down. Detergent that strips the natural oil from down barbules leaves them prone to sticking together and reduces loft recovery. Down-specific wash products (Nikwax Down Wash, Grangers Down Wash, or similar) use surfactants that clean the down effectively without stripping the natural oil coating. Some also contain a reproofing agent that restores DWR (durable water repellency) to the shell fabric simultaneously. The shell fabric of most down jackets has a DWR coating — a thin film of fluoropolymer or non-fluorinated polymer that causes water to bead off the surface. This coating is not waterproofing (down jacket shells are not typically waterproof), but it prevents light rain and snow from wetting out the shell and wicking toward the fill. DWR degrades with use and washing. Standard laundry detergent residues left in the shell fabric additionally impair DWR. Rinsing twice after washing removes most residue. Tumble drying at low heat activates the DWR coating (heat causes the DWR polymer to re-orient optimally at the fabric surface).