Get the steel lunch box.

Stainless steel is the better lunch box if you care about chemicals and keeping food fresh — plastic’s only real advantages are weight and microwaving.

On chemicals: modern plastic is mostly fine for cold, non-acidic food. But the moment it gets scratched, old or heated, it starts leaching more stuff than you want near your lunch. Steel is inert. There’s nothing in it to leach, ever. No BPA, no phthalates, no mystery.

On freshness: the seal matters more than the material, honestly. But steel doesn’t absorb odors or stains the way plastic does — your container will not taste like last Tuesday’s curry forever. It also holds cold better. Throw the empty steel box in the fridge the night before and your food stays properly cool until lunch, which plastic just can’t do.

The steel downsides are real: heavier, louder when you drop it, dents, and it’s a hard no for microwaves. Plastic is lighter and cheaper. So if you’re a microwave-your-lunch person who eats right away, plastic is fine. If you pack lunch and eat it later, steel wins every time.

For something you’ll use every day for years, steel is worth the extra few bucks.