Designed to keep rice at the right levels of moisture and warmth. Made of a soft, porous wood that absorbs excess moisture from the rice and keeps it from drying out. The tub's large, unfinished surface helps moisture to evaporate quickly so the rice ends up light and loose rather than sticky and gelatinized. And the thick walls and base of the sushi-oke keep the rice warm. The Chinese-made sushi-oke is a good value, but is not as finely made or of as high of quality as the Japanese-made tubs. 12 inch diameter, made in China.