You take excellent care of your down comforter -- fluffing it daily to restore the loft and protecting it with a washable duvet cover. But the day comes when it needs more TLC in the form of a good washing and a thorough drying. Drying is critical, because a down filling will grow mildew or mold if it sits around wet or damp. The delicate down clusters will clump together in a sodden mass that insulates no one, leaving your prized comforter sad, saggy, deflated and pretty much useless. Keep your feathers dry with a handy dryer and a clean tennis ball or a clothesline and some help from the weather.
There's no need for dry cleaning for most down comforters. Check the tag on yours to see if it can be washed -- in almost every case, that's the chemical-free option. Pop it into your washer at home if you have a large-capacity machine -- warm water, mild detergent, delicate cycle, two rinses. It's important to get all the soap out of the down.
Then shake out the comforter and pile it into an extra-large capacity dryer. You might need a laundromat to find a big enough machine. The comforter requires plenty of air circulating around it for complete drying -- and this could take several hours at the lowest dryer temperature. It's worth it. Any moisture will ruin your bedding, so bring a good book. Toss a clean tennis ball or two in with the comforter to help keep the soggy material from clumping together. Pull the comforter out of the dryer from time to time to shake it out and help distribute the drying down. Hold the duvet up to the light to check for visible shadowed clumps of down, a signal that it needs more drying time.
Hang a washed down comforter on a clothesline or drying rack on a sunny day to get that fresh-air smell in your bedding and save wear and tear on the duvet envelope and the environment. Spin the duvet for an extra cycle in the washer to get as much water as possible out of it. Sshake it thoroughly to fluff the down, and arrange it to get maximum air circulation.
This isn't a park-it-and-forget-it job; your down comforter is an investment, and occasional monitoring is part of the dedicated effort to keeping it in peak condition. From time to time, check on the comforter and reposition it on the line or rack to expose more area to sun and breeze. Stretch it over a couple of lines so the sides won't cling together and the top and bottom dry faster. Keys to making this work are a lot of sun and a brisk breeze, so choose your wash day carefully. If the comforter seems slightly heavy or damp at dusk, it will benefit from some time in the dryer on the lowest setting. Don't store a just-washed-and-dried down comforter immediately. Leave it out to breathe until it's dry as a bone.