Fill power is a great metric for comparing down products, but the fill power number alone cannot tell the full story. Another major factor is fill weight, which is the actual physical amount of down, by weight, that is used in a product. Additionally, the full composition of the down is important. Namely, what percentage of the down contains down plumage, also known as "down cluster," in relation to other elements, such as feather and quill? Down that contains high percentages of feather and other miscellaneous elements tends to be of lower quality.
