“Fill Power” is a critical indicator which reflects the insulation ability of feather & down products, which is also a measurement of the space occupied by a designated material. The higher fill power means it keeps more air volume, namely the better insulation ability. The international unit of fill power measurement is in³/30g, it says under certain conditions, the exact cubic inch of 30 grams of down occupied. Down content is closely related to fill power.

Professional explanation by Huaxiong, Wang

Fill Power is an indicator of measuring the quality of down washing, drying, and storing. Meanwhile, it’s also a key factor of insulation ability. Fill power is not a fixed indicator after years of observations and experiments. Longtime storage, pressure or freezing could reduce the fill power, but it could be recovered to some extent after proper treatments.