The dishwasher will warp that lunch box liner

Hand-wash that removable liner, because the dishwasher will warp it eventually.

Most lunch box liners are thin polypropylene or polyethylene. They’re fine at room temperature, but a dishwasher’s drying cycle pushes 150–170°F, and that’s enough to soften and deform the plastic. It might survive the first few washes, then one day the lid won’t seat right and you’ll wonder why you gambled.

Cleaning it right is easy. Rinse it out as soon as you get home so nothing crusts on, then wash with warm water and dish soap. If it’s stained or smells like last Tuesday’s tuna, let it soak with a little baking soda or white vinegar for ten minutes. Air-dry it fully, or at least towel it off, before you snap it back in — moisture trapped behind the liner is how you get that weird musty smell.

If the liner is genuinely labeled dishwasher-safe and you don’t have a hot-heat dry cycle, you can risk it. But the temp ratings printed on cheap plastic are optimistic. Hand-washing takes two minutes and removes the whole question.

A warped liner is the kind of repair you can’t actually repair.