All-steel lunch boxes are heavy and don't keep anything hot

Fully stainless lunch boxes exist, but every one of them is a single-wall metal tray that weighs a lot and does absolutely nothing for insulation.

The real options are EcoLunchbox, LunchBots, and PlanetBox. All three make bento boxes that are steel through and through — steel body, steel lid, steel latch or magnets, no plastic anywhere. That’s genuinely rare. But the price you pay is weight: most land around 1 to 1.5 pounds empty. A comparable plastic bento is a third of that. You’re hauling a brick in your bag.

Now the insulation part, because this is where people get burned: single-wall steel does not keep food hot or cold. It’s a heat sink. It conducts heat away from your food faster than plastic would. Your soup goes lukewarm by noon, your salad sweats all morning.

If you actually want temperature retention, you need a double-wall vacuum food jar — a Klean Kanteen, Stanley, or Thermos. Those are also all-steel (with a silicone seal, which isn’t plastic), and they’ll hold hot or cold food