How to Unclump a Down Sleeping Bag/Comforter
Clumped down can happen due to age or moisture getting into a down sleeping bag or comforter. This is especially common after washing the sleeping bag or comforter and not drying it properly.
When down clumps into sections the sleeping bag or comforter looses its ability to hold heat. Instead of an evenly spread layer of down, the down joins together into bunches. These bunches then leave a lot of empty space between each other. When this happens its like not having any down at all in sections of the bedding.
Though some would think that their sleeping bag or comforter is beyond repair, there is a simple way to make things better. To unclump the down, throw it into a dryer on the low setting and also throw in three or so tennis balls. This will tumble the sleeping bag or comforter around a bunch and while doing so the tennis balls will hit the clumps of down, destroying the clumps. As the clumps are destroyed the down spreads more evenly through the bedding restoring it back to normal.
Another option is to unclump the down by hand. Just grab the sections of the bedding where you feel the down is bunched up and pull and tug at them to release the down. I once had a down sleeping bag that I thought was useless because of the clumped down. The sleeping bag stopped being warm enough to use for most camping trips. Then my mother threw it into the dryer with some tennis balls. That sleeping bag is still being used today, over ten years later.
As with all materials, over time down losses some of its warmth. This is inevitable and will happen no matter what material is used. However, with proper care, a good down sleeping bag or comforter should last decades.