Things have never declared themselves empty, nor have they declared
themselves form; and they have not declared themselves right, wrong,
defiled or pure. Nor is there a mind that binds and fetters people.
It is just because...
ZAZEN MEDITATION GUIDE - Chapter 4. Cushions and Pads
Cushions and Pad You will need a cushion and a pad in sitting zazen. The pad is about 28 inches square, stuff with kapok or cotton batting so it will be about 1.5 inches thick. The cushion which is stuffed kapok or cotton batting, too, and about 12 - 18 inches in diameter and it flattens out like a pillow to set upon the pad. You may use a pillow if you wish.