Mollipilose

Having a fur or plumage that is soft or fine; fleecy, fluffy, downy.

Barn Owl (Tyto alba). If you’ve ever met a Barn Owl up close
you’ll understand why I choose this to illustrate
mollipilose: their feathers are just unbelievably soft,
which is why they are so silent in flight.

A surprisingly late first usage in 1890 which is derived from the Latin mollis, soft + pilus, hair.

H/T @HaggardHawks