Plastic or glass food containers? It's not really about the material you think

It's not about the material, it's about heat, grease and scratches

Plastic is a huge family of materials. Some types become food containers, some become water pipes, some become phone cases. They're not all the same.

For food containers, what scientists care about is migration: a very small amount of substances moving from the plastic into the food. That amount goes up when food is:

• Hot. Reheating in a box that isn't heat-resistant is the most common case.
• Greasy. Some substances in plastic dissolve better in oil than in water.
• Acidic. Dishes with vinegar, tomato or lime.
• Stored a long time.
• In an old box that's scratched, cloudy or warped.

In other words, the same plastic box holding cucumber in the fridge is a world away from holding hot curry that then goes in the microwave.

BPA: what's settled and what's still debated

BPA (bisphenol A) is the name that comes up most. It used to be found in some hard, clear plastics and in the inner coating of cans.

What's settled:

• In 2012, the US Food and Drug Administration (FDA) stopped allowing BPA in baby bottles and sippy cups.
• In 2023, the European Food Safety Authority (EFSA) re-evaluated BPA and lowered its tolerable daily intake to many times below the previous level.

What's still debated:

• The agencies don't fully agree with each other. The FDA still considers current BPA levels from food packaging to be safe.
• "BPA free" doesn't mean the box contains nothing else. Some replacement chemicals from the same family are still being studied.

We don't want to scare you. The sensible approach is to cut down on the situations that increase migration, not to panic over every single box.

Glass: heavy, breakable, but happy in the microwave

Glass releases almost nothing into food. It doesn't stain from curry or hold on to fish sauce smells. You can see straight through to what's inside.

But it has its downsides too:

• Heavy. Carrying five glass boxes to work is a light weights session.
• Breakable. One drop and it's over.
• Sensitive to thermal shock. Taking a box from the freezer straight into a hot oven, or pouring boiling water into a cold box, can crack the glass.
• The lid is usually still plastic. When reheating, take the lid off or rest it loosely on top, don't seal it.

Stainless steel boxes are durable, light and great for cold food and packed lunches. But stainless steel can't go in the microwave.

Give each box the right job: plastic for cold, glass for hot

Here's the simple formula we like to use:

And a few small habits:

• Don't reuse takeaway boxes, butter tubs or yogurt tubs for reheating. They're made for cold food and single use.
• Replace boxes once they're heavily scratched, cloudy, warped or cracked.
• Don't let cling film touch the food when reheating.
• Let food cool a little before putting the lid on a plastic box and refrigerating.

More on reheating is in reheating in the microwave the right way.

What does a good meal prep box look like?

Beyond material, the shape of the box affects both taste and safety.

1. Shallow and flat. Shallow boxes help food cool faster before it goes in the fridge, and reheat more evenly. The US Department of Agriculture (USDA) recommends dividing large amounts of food into shallow containers.
2. Tight lid. Keeps smells from spreading to other food and stops food drying out.
3. Compartments, or a small pot for sauce. Keep sauce separate and the veggies won't go soggy.
4. Same size, stackable. A tidy fridge lets cold air circulate more easily.
5. Room for a date. A strip of masking tape on the lid is enough.

No need for an expensive set. Four or five glass boxes for the dishes you reheat often, plus a few good plastic ones for cold food and freezing, is plenty to start.

Frequently asked questions