In reply to Dave 88:
as above but make sure it really is dry.
Down keeps you warm by trapping lots of air but it also traps lots of water. If not fully dried the down can go mouldy. A big down jacket on a low heat I would say take more like 2-3 hours to be totally dry. 1 hour and then air it rubbing any clumped spots to break them apart will also work. Just don't leave it in a wardrobe etc whilst it's still a bit lumpy.
Alternatively give it a day or two airing then another 15 minutes in a drier with the tennis balls.