The best soup carrier is a thermos, not a lunch box.

The best way to pack soup or stew without leaks is a wide-mouth vacuum-insulated food jar — a thermos, basically — not a lunch box.

Lunch boxes and bento containers say “leakproof,” but they mostly mean “won’t spill if you carry it flat.” Soup is liquid, hot, and generates steam. That’s a completely different test. A quality thermos like the Stanley Classic Food Jar, Hydro Flask Food Jar, or even the basic Thermos brand one will outlast every plastic tub you own. They have a screw-top lid with a silicone ring, and they’ll hold soup hot until lunch if you preheat the jar with boiling water for a couple minutes first.

If you also want a salad or sandwich on the side, that’s fine — use a separate container. But don’t try to make one box do everything. That’s how you end up with soup-soaked crackers and a mess in your bag. A thermos is the only thing that genuinely doesn’t leak, and you can test it by filling it with water, closing it, and turning it upside down over the sink. Do that before you trust it with lentil stew.

The good news: you don’t need to spend a fortune. Any double-wall stainless steel jar with a wide mouth and a real gasket will do. Just skip the cheap ones with the flimsy push-button lids — those are for coffee, not soup.