IKEA sells both duvets(the fabric cover for the comforters) and the comforters themselves (the stuffing/down quilted into a blanket). In the event that you needed to replace the stuffing inside a comforter it would be easier to buy a new one. If you had a duvet without a comforter inside it IKEA has a wide selection of options with different weights and fillers.
Stuffing? That would be a lot of work. You'd have to go to Wal-Mart, Jo Anne's fabric or maybe even Michael's.
Just get a new one
IKEA does not sell stuffing
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