Higher fill power (AKA loft) mean that the down clusters are larger.
The larger the down cluster the higher the quality.
The higher the quality the longer it will retain it's loft and firmness.
The larger the down cluster the more mature the bird from which it came.
The larger the down cluster the more air it traps.
The larger the down cluster the more it will loft and puff up.
The larger the down cluster the better the insulating power.
The larger the down cluster the lighter the down pillow, down comforter or feather bed will be.
