Our insert pillows are made of Ply-a Soft Polyester:
It is a very limp poly that will not bounce back after it set in a position. It is “moldable” since it is so limp. It will hold a V shape (karate chop) across the center of the pillow giving the look of down and feathers, but not the expense. Feel: limp, not bouncy, ideal for making a V top shape pillow. Very soft and comfy too.