https://www.dxhdmetextiles.com/product/throw-pillows-and-seat-cushions/
The filling determines much of a pillow's softness, loft, recovery, and overall shape. If the filling is too loose, the cushion may appear flat after use. If it is excessively firm, it may lose the relaxed appearance expected from a decorative pillow.

Instead of requesting a general specification such as “soft filling,” buyers can work with manufacturers to define the desired feel and appearance more clearly. Filling material, quantity, distribution, and inner construction should be considered together.