General:
* Downy
* Plump
* Plush
* Silky
* Feathery
* Cushiony
* Cloud-like
* Ethereal
More specific:
* Powdery (for feathers that shed a fine, dusty powder)
* Gossamer (for very fine and delicate feathers)
* Fluffy (for feathers that are light and airy)
* Bouncy (for feathers that spring back when compressed)
* Insulating (for feathers that provide warmth)
The best word to use will depend on the specific context and the feeling you want to evoke.