Gently place a washable comforter or goose down duvet in the washer. If you are having a hard time fitting your down comforter or goose down duvet into the washing machine, do not force it in. Go to a self-service laundry and use a larger washer that is more suitable for your comforter or duvet.
Wash with cold water on a gentle cycle with a detergent made for down comforters or fragile hand washable clothes.
Place two tennis balls into the dryer prior to adding the goose down duvet. These will help fluff up your comforter. Dry the down comforter on low heat to prevent scorching feathers. It may take several hours for your comforter to dry. To reduce time in the dryer, air-dry your goose down duvet outside for a few hours prior to running it through the dryer.
Hand wash your goose down duvet or comforter if it's extremely fragile and you can see feathers starting to come out. Submerge the comforter in a large sink or the bathtub with mild detergent. Rinse thoroughly. Air-dry in sunlight for a couple of days.