Get a real thermos, not Tupperware

The trick to packing hot soup without leakage is a wide-mouth vacuum thermos — not a plastic container with a snap lid.

Plastic containers fail for two reasons: the lids aren’t really watertight under pressure, and hot liquid creates steam pressure that pops seals. Even a “leakproof” deli container will betray you in a backpack.

A wide-mouth vacuum thermos (Stanley, Yeti, Thermos brand — any of them work) solves it. Preheat it by filling it with boiling water for a few minutes, empty it, then pour in your soup piping hot. Leave a little headroom at the top — filling it to the absolute brim makes the lid leak. Screw it on tight.

Bonus move: wrap the closed thermos in a kitchen towel before it goes in the lunch box. It catches minor condensation, adds insulation, and acts as a buffer. And test any new thermos at home with water before you trust it with soup — not all seals are created equal.

Your bag will thank you.