Make sure your gear is completely dry before storing it. Moisture, mold, and mildew are the enemies of down products. At best, they’ll give your bag or garment that signature blue cheese smell, and at worst they can rot the down.
Avoid storing your gear compressed. The best way to store a down bag is to hang it up somewhere dry and ventilated, but you can also use a large cotton or mesh storage bag.
Store your gear in a warm, dry room with decent airflow to prevent the growth of mold and mildew and stop your kit from picking up musty odors.
Use a dedicated down wash instead of regular detergent. Regular detergents can leave behind residue that hinders down’s insulating and breathable properties.
Wash your gear in a front-load washing machine or by hand. If you have a top-load washing machine, wash by hand because top loaders can be rough on down.
Dry your gear properly by laying it flat on a drying rack for a couple of hours - avoid direct sunlight.