Stick with glass or #5 plastic

Glass is the safest lunch box choice for microwave reheating, and #5 plastic with the microwave symbol is the next best thing.

Flip the container over. The rules are stamped or molded right there. You want to see either the words “microwave safe” or the little icon with three squiggly wavy lines. If neither is there, don’t gamble on it — that’s how you end up with a warped lid and a weird chemical taste in your pasta.

For plastic, the recycling number matters. #5 (polypropylene) is the good one — it handles heat without melting or leaching much. #1 and #6 are the problem children. #7 is a grab bag of mystery plastics, so avoid it unless it’s explicitly labeled. Glass and ceramic are almost always fine, but skip anything with metallic paint or gold/silver trim — that sparks.

Even a “safe” container has limits. Retire plastic that’s scratched, cloudy, or stained, because heat makes old plastic leach more. Don’t seal the lid when reheating — vent it, or cover with a paper towel. And safe doesn’t mean cool; that plastic gets hot.

When in doubt, glass.