Like down pillows, down-filled couch cushions flatten over time, making them a bit less comfy than when the down was fluffed up to its fullest. Down-filled furniture is subject to a lot of weight from people sitting upon it, which means compressed cushions unless the cushions are fluffed up frequently.
You've Got the Beat
Remove all seat cushions, removable cushions and pillows from the couch. Vacuum the couch to pick up dust and debris that has fallen between the couch cushions.
Hold one of the smaller down cushions or pillows between both hands along opposite edges and push towards the center. Rotate the pillow and continue squeezing and pushing towards the center to redistribute the down. Repeat this process with each cushion small enough to manage between your hands.
Hold a large cushion, such as a seat cushion, so one end is on the floor and the other end is supported upright by your hand. Kick and hit the cushion a bit in various places, rotating the pillow as you work. Squeeze from the top down or side to side so more down moves toward the center, repeating the process with each rotation of the cushion. Hit the other side of the cushion as well. Repeat the process with all cushions.
Feel the areas of the couch, such as the backrest, to determine if they need fluffing up. Slide your hand or arm across the backrest or armrest to smooth out lumpy areas and redistribute the down.
Wash it Up
Unzip cushions and remove the inner pillow-like structure. If all the stitching is intact and the pillow can withstand a trip through the wash, toss it into the washing machine and wash on a delicate cycle with a small amount of laundry detergent. Place two cushions in at a time, if possible, for a more balanced load.
Place a few clean tennis balls in a pillowcase and tie a knot in the end. Place the pillowcase with balls, as well as the couch cushions, in the dryer using a gentle cycle.
Check the cushions every 15 minutes or so and fluff them by hand. Place them back in the dryer until they dry completely. Fluff them up again as you place them back into their upholstered cases.