When making Bento boxes?

When you make a Bento box and you put something warm in it, is the idea to eat it cold later or do you heat it up? Or do you get a special box that means things won't go cold??|||You can heat it up later if you want. Or you can also get insulated bento boxes for hot or warm food. This way the food can stay warm.

But generally, bento foods are supposed to be eaten cold. Thats why they usually put foods that don't need to be heated up.

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