Glass and #5 plastic are your microwave lunchbox picks.

For microwave reheating, stick with glass, ceramic, or #5 polypropylene plastic, and skip anything with metal trim or melamine.

The little symbol you’re looking for is a microwave with wavy lines, or just wavy lines under a dish icon. Some brands also just print “microwave safe.” That means the container passed basic testing — but it’s not a guarantee that every lid or compartment is safe too. Lids are often the weak point, so check them separately or just take them off.

If there’s no symbol, use the recycling number. #5 polypropylene is your safest plastic bet. Avoid #1 (PET), #3 (PVC), #6 (polystyrene, as in foam takeout boxes), and #7 (often contains BPA). Glass and ceramic are almost always fine — unless they have metal rims, gold details, or plastic handles.

One more thing: even microwave-safe plastic will eventually warp or stain, and it’s not great for greasy, high-fat foods that get very hot. Glass is the better long-term choice if you can handle the weight.

When in doubt, reheat in a glass bowl you already own and use the fancy lunchbox just for carrying.