[sushi_78]

I don't think that kind of cardboard is an issue even if chewed. The rule I go by is that if the ink runs when the cardboard or paper is damp, it isn't safe. Most printer inks for home use will run, as well as newspaper ink, so avoid paper printed with those. Commercially printed cardboard is usually fine. Frozen food boxes can have a waxy coating, so I would avoid those boxes.