In reply to chris fox:
and, if you don't have tennis balls, you can wash in the machine without them on a gentle cycle & slow spin and, as the garment air dries slowly, shake it regularly. I've done this 3 times now with no problems to any of the 3 jackets washed - certainly no persistently clumped down. Takes 3-4 days to dry fully, but our flat is quite cool - no doubt would be faster with an airing cupboard or a warm house.