Check the bottom, not the brand

Most plastic lunch boxes are fine to microwave, but the only way to know for sure is to flip it over and find the microwave-safe symbol.

That symbol is a little square with wavy lines inside, sometimes printed with “MICROWAVE SAFE” underneath. No symbol means the manufacturer didn’t test it, and cheap plastic can warp, melt, or leach junk into your food. Don’t gamble on it.

The recycling code matters too. #5 polypropylene is the best plastic for reheating — it handles heat and doesn’t warp easily. Avoid #6 (Styrofoam) and #3 (PVC). #1 is okay for a one-off but will stain and warp after enough cycles, so don’t count on it long-term.

And even with a safe container, don’t seal the lid tight. Vent it, or pressure builds up and you get a mess or a steam burn. Oily and tomato-heavy food will also stain and hold odors in plastic, no matter what the label says.

For anything saucy or greasy, a glass container is the better choice. Plastic is for boring leftovers, not marinara.