The Fill Power indicates the fluffiness and volume grade of the down in a scale of 400 to 900 cu-in (cubic inch).
In order to obtain this data, 30 grams of down are introduced in the cylinder of an authorized machine to calculate the Fill Power. The down is compressed in determined parameters and at the end of the process the reached volume is shown.
A high Fill Power down quilt will be light and fluffy, and it will have maximum thermal insulation with the minimum weight. On the other hand, a different down quilt with inferior Fill Power will need higher weight to have the same thermal insulation.
In the picture below it is possible to see the volume variance of the different down qualities. All tubes have the same amount of down, however, the better the quality, the higher volume is obtained. Therefore, a duvet´s quality is given by the lightness and comfort provided by a down which has a high Fill Power.
A correct choice in the weight depending on the quality of the down according to it´s Fill Power, in addition of providing extraordinary thermal insulation, assures an effective evaporation of the humidity generated during the sleep.
Downs origin is determinant in the quality of it. The best qualities are from Europe and Canada, on the contrary, down from Asia is much smaller and heavier, giving inferior Fill Power values.