What are the fill powers of the Duvets? Administrator 28 August 2023 20:58 Updated The fill powers refer to the amount of space an ounce of down will occupy when the down is at its maximum loft (or fluff)! The Down Duvet has a fill power of 600 cubic inches, and the Humidity Fighting Duvet has a fill power of 750 cubic inches. Related articles Do I need to use a duvet cover with my Casper Duvet? What kind of down is the Duvet made from? How do I care for my Casper Duvet? Is the Dog Bed waterproof?