It says right on the label that it is filled with shredded polyurethane foam. Even before reading the label I recognized the fill by its lumpy feeling. I had a very cheap pillow with such filling once. I did not use it to sleep on and finally threw it away. The "patented interlocking fill" is just hype.
*However* this shredded foam seems to be to certain specifications. The genius to this pillow is partly the marketing and partly the ordering and care instructions.
On the order form, you are supposed to choose a pillow by T-shirt size. If you wear your t-shirt tight, choose a larger size to get the correct pillow. This actually works.
The instructions say to tumble the pillow on high heat before using. That fluffs it up nicely. Washing and drying on high heat also works well.
After my initial disappointment at the shredded foam fill, I am now quite happy with the pillow because it actually performs quite well. It is more supportive than the higher-line polyester pillows, IMO, while it is also soft. It is possible to shift fill to preference.
I suggest fluffing up the pillow each morning or evening before use, and you may be surprised how well it works.