Buy glass. Skip the plastic lunch box.

Glass is the best lunch box material for microwaving, and it’s the only one you can take from freezer to microwave without worrying about chemicals.

Plastic labeled “microwave safe” only means it won’t melt in the microwave. It doesn’t mean it won’t leach chemicals—especially when you’re heating something oily or acidic. And the older the container gets, the worse it gets. Scratched plastic leaches more. Worn lids leach more. Glass just doesn’t have that problem at all.

The standard answer is tempered glass: Pyrex, Glasslock, or Anchor Hocking all make freezer-to-oven containers with snap-on lids that are perfect for this. And no, they won’t explode in the microwave—but they can thermal-shock if you go straight from freezer to full power. Let the container sit on the counter for five minutes first, then microwave on medium. That’s the only real risk, and it’s easily avoided.

One more thing: take the plastic lid off before you nuke it. Cover with a paper towel or a vented silicone lid if you need to stop splatter.

Your lunch isn’t the place to gamble on mystery chemicals.