Fill power measures the loft of a down product, which is essentially the quality of the down. Maximum loft occurs when the down clusters are fully expanded. The fill power rating value is calculated by measuring how many cubic inches an ounce of down creates at its maximum loft. A down fill rating of 600, for example, means that one ounce of down can cover 600 cubic inches.
Fill weight is a measure of the total weight of the down inside the jacket. Fill weight signals quantity. For example, a jacket with 12 oz fill weight means that 12 oz of down was used in the jacket.
The fill ratio is a measurement of the down to feather ratio of the down insulation. The fill ratio calculates the percentage of down to the percentage of feathers in the product. The first number represents the percentage of down, and the second number represents the percentage of feathers. Generally speaking, a higher first number means a higher quality (and more expensive) product. For example, a down jacket with an 80/20 fill ratio implies that it comprised of 80% down and 20% feather. As down is more expensive than feather, with all else being equal, a jacket with an 80/20 fill ratio will be warmer than a jacket with a 70/30 ratio.
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