Top-rack only is a real warning

If your lunch box says top-rack only, don’t put it on the bottom rack.

The label is not a suggestion. The bottom rack sits right next to the heating element and gets hit with hotter water and stronger jets. Most lunch boxes are made of plastic that isn’t rated for that kind of heat. You risk warping the shape, cracking the lid, or destroying the seal that keeps liquids inside. Some plastics can even leach chemicals at high temperatures, which is a whole other problem.

The top rack is farther from the heat and the spray isn’t as aggressive. That’s why manufacturers put the “top-rack only” note there in the first place. And if you do use the top rack, make sure the lunch box is lying flat and not upside down, so it doesn’t fill with water and stay soggy.

Your lunch box is not where you save a few minutes. Read the label, use the top rack, or just hand-wash it.