Fill power is used to measure the goose and duck down quality.

To measure Fill power the following test is made:
1 ounce (28.4 grams) of down at a certain temperature and humidity is placed in a measuring cylinder with a diameter of 241 mm and the top is placed under pressure of 68.3 grams for 3-5 days. The volume that will occupy the down after passing this test is an indicator of its density and Fill Power.
After passing this test, the results of the Fill Power parameter are distributed as follows:
less than 400 – low quality
400 – 450 – medium quality

500-750 – good quality
750 and higher – down of the highest quality

The higher Fill power, the more air contains the duvet, pillow or sleeping bag and coat. The higher the fill power of a down jacket or sleeping bag, the warmer it will be with less weight.