Down jackets and coats are excellent protection in cold, dry temperatures. They are well-insulated and can keep you warm in some of the coldest weather. Down comes from the under feathers of birds like ducks and geese. Because birds must be very lightweight to fly, the down is at once very warm and very light, trapping air and creating an insulating barrier to cold. As long as it doesn't get wet, down remains very warm. Because down can be destroyed when wet, it is important to wash and dry it carefully.
Wash your jacket on the gentle setting of a front-loading washer. A front-loader is preferred because it does not have an agitator in the middle. Use a laundromat washer if you need to. If you can't get to a front-loader, wash your jacket in a top-loader alone.
Choose a lightweight "safe for silk" detergent for your jacket. Woolite is the known name-brand, but many generic brands are available for gentle washing. This is important because heavier detergents can attach to down feathers, weighing them down and causing them to lose their loft. Special soap also is available for down at speciality outdoor stores, but it can be expensive.
Rinse your jacket twice before drying to be certain that all of the soap is removed. When you move the jacket from the washer to the dryer, be sure to move it as one piece, carrying it from the bottom. Pulling it out at one end will force much of the down to the bottom of the jacket, and will make it much harder to dry and keep lofted.
Tumble dry your jacket, preferably in a large, commercial dryer on low heat for at least four hours. Place two tennis balls in the dryer with your jacket to help continually loft the jacket while it dries.
Don't used spiked dryer balls to loft your jacket. This could severely damage it.