Read the bottom of the lunch box before it goes anywhere near a microwave

Whether your lunch box survives the dishwasher or microwave depends entirely on what it’s made of, so flip it over and read the symbols first.

Most plastic lunch boxes have a little triangle symbol on the bottom. If it shows a plate or cup with water droplets, it’s dishwasher-safe. If it shows wavy lines or says “microwave safe,” you’re good for the microwave. If you see neither, don’t push it. Plastic that isn’t rated for heat can warp, crack, or leach chemicals into your food, and there’s no way to tell by looking.

Stainless steel and insulated lunch boxes are the ones people mess up most. They’re almost always fine in the dishwasher — unless it says hand wash, the lids have rubber gaskets that hate the heat. But never, ever put metal in the microwave. It sparks and can literally start a fire. Glass is fine in both, but the plastic lid usually isn’t, so take it off. Silicone is basically invincible and handles both fine.

And if it’s a fabric lunch bag or a bento-style soft container, skip both appliances and wash it by hand. “Dishwasher safe” also doesn’t mean “use the heated dry cycle every night” — top rack, low heat, and your plastic will last a lot longer.

Ninety percent of ruined lunch boxes died in an appliance their owner assumed was safe.