Freezing a lunch box overnight is fine — check the plastic first.

Yes, you can chill most lunch boxes overnight in the freezer, but the material matters more than you’d think. Do it right and you get a built-in ice pack. Do it wrong and you get a cracked container.

Hard plastics are your safest bet. Look for the recycling number: #5 (polypropylene) and #2 (HDPE) both handle freezing fine. Silicone is also great, and stainless steel works perfectly — just don’t fill it all the way if you’re freezing liquid, since it expands.

Glass is okay too, but needs more care. Leave some headroom and don’t go from boiling food straight into the freezer. The real thing to avoid is brittle plastic like #6 polystyrene — that’s the cheap clear stuff that shatters when it gets cold. And if your lunch box has a super airtight seal, don’t tighten it completely before freezing, or the lid could pop off from pressure changes.

So check the bottom for the recycle number, and you’re good. Future lunch you will thank you.