Glass and stainless steel survive the dishwasher. Plastic is a gamble.

Glass and stainless steel lunch boxes are the only ones you can reliably run through the dishwasher without warping, leaking, or wrecking the lid.

Plastic is the problem. Polypropylene (#5 PP) is technically dishwasher-safe, and you’ll see it stamped on the bottom of most containers. But the base usually holds up while the lid doesn’t. Thin lids warp in the heat, the seal bends, and suddenly your “leakproof” box is leaking soup all over your bag. Cheap containers from generic brands take two or three washes before the clips refuse to snap shut. Tritan and other “premium” plastics do better, but you’re still betting on a thin plastic latch.

For glass, look for tempered borosilicate-style bodies—Pyrex Snapware, Rubbermaid Brilliance, Ello, or the IKEA 365 series. Put the glass part on the bottom rack, no problem. The lids are the weak point: they’re almost always plastic with a silicone gasket, so run them on the top rack only, and if the gasket comes out, hand-wash it. One more rule: don’t stack them airtight while hot. The cooling air creates a vacuum that pops the seal or sucks the lid inward.

Stainless steel is great until you check the lid. Many are plastic, same risk as above. Fully sealed stainless with a silicone lid—like the ones from LunchBots or Bentgo—is basically dishwasher-proof. A cheap stainless container with a plastic locking lid will warp just like the plastic ones.

Bottom line: buy glass or stainless bodies and expect to replace silicone gaskets after a year of machine washing. The dishwasher eats cheap plastic—spend the extra few bucks on glass.