A Sushi chef at a Sushi restaurant at Westchester County at New York once told me that Japanese rice still stick and hold shape when it is cold. But other rice when hot it sticks and hold shape together but once cold will not stick and not hold shape well. When making musubi or onigiri hands are used to shape rice, and obviously cool down cooked rice so that is easier to handle by hands. But not using Japanese rice making musubi or onigiri may be difficult because at cool temperature where rice can be handled by hands it may not stick and hold shape.

Ths is according to the sushi chef at Westchester county.