It is made of sweet or salty-sweet boiled aburaage, which is opened into the shape of a bag and stuffed with sushi rice (vinegared rice) or sushi rice mixed with ingredients like carrots and mushrooms.
甘くあるいは甘辛く煮付けた油揚げを袋状に開き、寿司飯（酢飯）をそのまま、あるいはニンジンやシイタケなどの具材を混ぜ込んで詰める。