Almost everyone who switches away from plastic food storage changes the box.
Very few people look at the lid.
Which is strange, because your food spends three days in the fridge pressed directly against it. If you care what your dinner is stored in, the lid is not a detail. It is half the container.
So what is it made of?
In the overwhelming majority of cases: polypropylene.
Polypropylene, or PP, is a thermoplastic. It is cheap, it is light, it is easy to mould into a shape that clips, and it is the default lid material for essentially the entire food storage category — including the parts of that category that market themselves as alternatives to plastic.
We are not going to tell you polypropylene is dangerous. Nobody can honestly tell you that.
We are going to tell you it is there, because most brands won’t.
Steel containers and bottles
These are brands you would reasonably assume had solved the plastic problem. From their own product pages and FAQs:
- Hydro Flask: “All of Hydro Flask’s caps are made out of BPA/BPS free polypropylene.”
- Chilly’s: steel outer, with a polypropylene component in the cap.
- Stanley: polypropylene lid. Several models add a plastic straw.
- Mepal Campus RVS: steel body, plastic lid.
- IKEA 365+ (steel): plastic lid.
- Klean Kanteen — the most credible plastic-free brand in the category — ships polypropylene caps as standard. The cap that isn’t plastic is a paid upgrade.
And one that goes further than the lid. Zojirushi’s flagship Ms. Bento is a steel vacuum shell — but the food itself sits in what their own listing calls “3 microwaveable inner bowls… made of BPA-free plastic.” The steel is the thermos. The plastic is the bit that touches lunch.
Glass containers — and this is the part nobody expects
Glass is a good material. We are not going to pretend otherwise: it is inert, you can see through it, and it goes in the oven. If your container never leaves the kitchen, glass is a genuinely fine choice.
But we checked fifteen glass brands sold in the Netherlands.
Every single glass container designed to be carried and sealed has a plastic lid. Not most of them. All of them.
- IKEA 365+ (glass): “Lid: Polypropylene plastic. Seal: Silicone rubber.”
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Mepal (glass): materials field reads
Glas, PP, TPE. - HEMA glazen clipdoos: “doorzichtige kunststof deksel.”
- Glasslock: “the lids are made of polypropylene.”
- Pyrex, Duralex, OXO, Anchor Hocking: “BPA-free plastic” — and none of them will name the polymer.
The only genuinely all-glass lids belong to canning jars — Weck, Kilner, Le Parfait — and their own makers tell you not to use them for daily storage. Le Parfait advises replacing the rubber seals every six months with everyday use. Weck’s own freezer instructions require their plastic Keep Fresh Cover.
And Pyrex proves the gap by failing to fill it. They built a glass-lid range — and dropped the leakproof claim.
In this category you can have leakproof, or you can have no plastic. Almost nobody offers both.
What their own FAQs say about those lids
We do not need to attack anybody. They have already written this section themselves.
- Pyrex: “The plastic material the covers are made of is porous and may retain colors and/or odors… This is a natural characteristic of the material and cannot be controlled.” They also advise against storing strong-smelling foods like onion or garlic. And: “My cover has warped. Can I straighten it? NO.”
- Anchor Hocking: “Sealing the cover may create excessive pressure causing the cover to melt, warp or cause personal injury.”
- Glasslock: “the gaskets are not available as a separate replacement part.”
A lid that is porous, that retains odours, that cannot be straightened once warped, and whose seal cannot be replaced — sitting on top of a container sold on the promise of being inert.
Glass solved the box and forgot the lid.
Ours is steel
Body, lid, divider — and the bottle cap.
That last one is worth pausing on, because almost every steel bottle on earth, at any price, closes with polypropylene. Ours doesn’t.
There is one non-steel part, and we will name it before you find it: a food-grade silicone seal, so it doesn’t leak. Silicone is not plastic, but it is also not steel, and you are entitled to know it is there. It eventually wears out, so we sell you a spare — for a few euros, for as long as you own the product.
Two materials. Both named. That is the entire list.
We say two, out loud, because nobody else in this category would ever volunteer a number greater than one. They all round down.
We would rather you counted.
See the whole category, lid by lid →
Food should be stored without doubt.
Every quotation above is taken from the brand’s own published product page, FAQ or materials listing, current as of July 2026.