You should not microwave a bamboo lunch box. Bamboo is a natural material that can be sensitive to extreme temperatures, including heat from a microwave. Microwaving a bamboo lunch box can cause the bamboo to dry out, crack, or even catch fire.

Bamboo lunch boxes are typically not designed for microwave use, and the high temperatures and moisture in the microwave can damage the bamboo and any finishes or coatings applied to it. Additionally, some bamboo lunch boxes may have metal components or fasteners, which can also cause sparking or damage in the microwave.

If you need to heat your food, it's best to transfer it to a microwave-safe container or dish before microwaving. Look for containers made from materials specifically labeled as microwave-safe, such as glass or microwave-safe plastics.

Always follow the manufacturer's instructions and guidelines for the proper use and care of your bamboo lunch box to ensure its longevity and safety. Remember that bamboo lunch boxes are ideal for cold or room temperature food storage and transportation, but they should not be used for hot foods or in the microwave.