The thermos wins for hot soup.

A vacuum-insulated thermos is the best call for keeping soup hot till lunch. The insulated-box-with-a-bowl thing is fine for salads or bento stuff, but it’s fighting physics when it comes to liquid.

Here’s the deal: soup has a lot of water, and water steals heat fast. An insulated bowl in a soft lunch box might keep things warm for an hour or two if you’re lucky, but every time you open the lid or the bag shifts, heat escapes. Vacuum insulation works differently — it basically eliminates air transfer, so that soup is still steaming at noon if you packed it at 8 a.m.

Get a wide-mouth thermos, not a narrow one. Soup with chunks needs room for a spoon, and wide mouths are way easier to clean. And do the trick of filling the thermos with boiling water for a minute before you add the soup — that pack of a pre-heated liner buys you another hour easily.

For most people, a decent 16-24 oz thermos is the answer. It’s not the cutest option, but “hot soup at lunch” beats “lukewarm soup that tastes like the inside of a bag” every time.