SmarTasty
Count calories with a photo
Glass, stainless steel or vacuum? What matters when you reheat food in plastic tubs, and which meal prep containers work best day to day.
Short answer: Glass is the easiest option for storing and reheating, stainless steel is best for taking food with you (but not for the microwave). You don't need to throw your plastic tubs away – just tip the food onto a plate or into glass before heating, because a lab study found the highest release of micro- and nanoplastics in the microwave. Melamine or "bamboo" tableware isn't suitable for hot food.
For how to set up meal prep in the first place, see the guide Meal prep for beginners: weekly plan & tips.
A study from the University of Nebraska (Hussain et al. 2023) looked at how many micro- and nanoplastic particles are released from polypropylene containers and reusable pouches into food simulants:
Putting it in context: the tests used water and diluted acetic acid, not real meals, and cell damage appeared in the test tube only at very high concentrations. What this means for your health is still open – but it's a good reason to decant your food all the same. On top of that, oily sauces or cheese get much hotter in the microwave than the rest of the meal and put more strain on plastic.
In 2023 the European Food Safety Authority (EFSA) cut the tolerable daily intake for bisphenol A (BPA) by a factor of 20,000, to 0.2 nanograms per kilogram of body weight. The EU then banned BPA and other bisphenols of concern in food contact materials with Regulation (EU) 2024/3190; the general transition period ended in July 2026, with deadlines up to January 2028 for some uses.
So new containers sold in the EU are BPA-free. But "BPA-free" doesn't mean nothing transfers when you heat them: the particles in the study above came from polypropylene, a plastic that contains no BPA.
The label mainly means the container survives the microwave under certain conditions and stays within the legal limits – not that nothing transfers whatever the dish and however long you heat it. Fatty and acidic foods, long reheating times, old scratched containers and heating the same box again and again are all less than ideal.
| Factor | Why it matters |
|---|---|
| Heat | can affect the material's structure and migration |
| Fat | picks up certain substances more easily than water |
| Acid | can put more strain on surfaces |
| Age of the container | scratches and clouding mean more wear on the material |
| Reuse | frequent heating speeds up wear |
Meal prep dishes almost always contain oil, dressing, cheese or sauce – which is exactly what makes plastic less appealing than glass for reheating.
Lunchboxes and bowls made from melamine-formaldehyde resin, often sold as "bamboo" tableware with bamboo fibres, are light and hard to break. The BfR (German Federal Institute for Risk Assessment) advises not using them for hot food and not in the microwave: at high temperatures, especially with hot, acidic food, melamine and formaldehyde can transfer into the food, and products with bamboo fibres released even more on average. For cold or lukewarm food, the BfR doesn't expect any health effects. More in the guide Cooking spoons & spatulas.
| System | Strengths | Weaknesses |
|---|---|---|
| Borosilicate glass | heat-resistant, ovenproof (check the manufacturer's instructions), doesn't stain, doesn't hold smells | heavy, can break |
| Stainless steel (insulated or single-walled) | sturdy, light, long-lasting, keeps food hot or cold for a long time | not for the microwave |
| Vacuum systems | less contact with air, stays fresh for longer | extra effort, no substitute for chilling |
At home, glass is usually the best choice; for commuting, school and the office, stainless steel; vacuum when you prep several days ahead.
Glass doesn't react with acid, doesn't take on smells and hardly stains from curry or tomato sauce. Borosilicate glass copes with changes in temperature better than ordinary glass – but still avoid big jumps, such as straight from the freezer into a hot oven. When buying, look for: borosilicate rather than pressed glass, tight lids with a silicone seal, stackable shapes and replacement lids you can buy separately. Ideas to fill them: Mediterranean recipes, high-protein recipes, meal prep recipes.
Stainless steel is sturdy, light and long-lasting; soups, stews or porridge stay warm for a long time in insulated containers. But metal doesn't belong in the microwave because it can spark – so at the office, tip your food onto a plate or into a glass bowl first. More on materials in the kitchen: Healthy cookware: Teflon, cast iron & stainless steel.
Less oxygen means texture, colour and aroma last longer – for prepared salads, cut fruit, cooked pulses, overnight oats or toppings such as walnuts. How much longer depends a lot on the food and your fridge, so don't take claims like "five times longer" literally. Vacuum is no substitute for chilling.
| Dish | Why it's a poor fit |
|---|---|
| Tomato sauce with olive oil | acid plus fat |
| Curry with coconut milk | high fat content |
| Bakes with cheese | hot pockets of fat on the surface |
| Salmon or chicken with sauce | fat and cooking juices |
More on fats: Omega-3 vs omega-6: which oils and fats to choose.
How the microwave, air fryer and oven compare: Microwave & air fryer.
Dull or whitish patches, scratches inside, stained edges, a smell that won't go, a warped lid. Containers like this are still fine for dry food such as nuts, but not really for heating.
Common mistakes: heating food straight in the plastic tub or under cling film; putting stainless steel in the microwave; using "bamboo" tableware for hot soup.
| Container | How many | Use |
|---|---|---|
| Medium glass | 4–6 | lunch portions |
| Small glass | 2–4 | sauces, toppings, snacks |
| Large glass | 2 | family portions, salads |
| Insulated stainless steel | 1–2 | taking hot dishes with you |
| Vacuum container | optional | longer storage in the fridge |
More on planning and shelf life in the meal prep guide.
Yes. For dry, cold food and short storage, plastic is much less of an issue: nuts, rice cakes, bread, dry toppings, fruit for the same day. It's less suited to anything oily, hot or acidic.
Glass costs more than basic plastic boxes, but good-quality glass often lasts much longer; stainless steel is usually the longest-lasting option on the go. Start with 4 to 6 glass containers and add more later rather than buying everything at once. Keep using your existing plastic tubs for dry and cold food.
New containers in the EU are BPA-free. But other substances and microplastics can still transfer when you heat them – in one lab study, most of all in the microwave. Decanting your food is the simpler, more cautious option.
Yes, that's much better than heating it in the plastic container.
Usually not for hot food: many are made from melamine resin with bamboo fibres and, according to the BfR, shouldn't be used for hot food or in the microwave. For cold snacks they're fine.
That depends on the dish, hygiene and the temperature of your fridge. Many cooked dishes keep for a few days; eat fish or moist salads sooner.
Usually less so than rigid plastic boxes, because they aren't the main contact surface for hot food. Replace them if you see signs of wear.
When it comes to materials, there's no need to panic – just a few simple habits: store and reheat in borosilicate glass, carry in stainless steel, use vacuum when you need it. Don't heat warm, fatty or acidic food in plastic, use melamine and "bamboo" tableware only for cold food, and keep your existing plastic tubs for dry food.