Wooden and bamboo bento boxes are made from wood which can expand and contract if excessive moisture is applied. To clean simply use a soft damp cloth to remove any remaining food. Then add to the cloth a mild detergent to remove any oil or remaining food. Towel dry after cleaning, don’t allow pools of water accumulate in the bento box. Do not submerge in water.
How do I clean wooden bento boxesKatachiware Japanese Style Tableware