Ziploc bags vs glass containers
Are plastic storage bags worse than glass containers?
The verdict
Glass, and the mechanism is contact area. A bag presses film against the entire surface of the food; a container touches the base and sides of whatever is sitting in it. LDPE bags were among the products NIST measured shedding trillions of sub-100 nm particles per litre into water.
Glass body with a polypropylene lid
60% confidence
These carry different evidence grades. Ziploc storage bag is grade B and Pyrex glass storage container is grade C. One component of our score is measured release, which only earns points where a laboratory has actually counted particles — so a product nobody has tested scores lower than an identical one that has been. Part of the gap you are looking at is a difference in how much anyone has looked. Why we do it this way →
Where they actually differ
| Ziploc storage bag | Pyrex glass storage container | |
|---|---|---|
| Contact geometry | Film against the whole food surface | Food sits in a rigid inert vessel |
| Fatty food | The worst case — many film additives are fat-soluble | No effect |
| Reheating | Not designed for it, and people do it anyway | Lid off, and it is the right container for the job |
| Freezer use | The most common use, and the least studied | Works, with headspace for expansion |
Where this comparison stops being reliable
The NIST work was done in deionised water, not on food in a freezer, and freezing has barely been studied at all. We know LDPE sheds in contact with water; the number for a frozen chicken breast does not exist.
The full picture on each
Does Ziploc storage bag have microplastics?
Yes. LDPE food-storage bags are one of the specific product types NIST measured shedding trillions of sub-100 nm particles per litre into water in ordinary use — and a bag presses film against the whole surface of whatever is inside it.
Full score breakdown and sources →
Does Pyrex glass storage container have microplastics?
Barely. The glass body is inert whether it is cold, hot or acidic, and it is the correct answer for reheating. The lid is plastic — so reheat with the lid off, and the only remaining polymer contact is the seal touching the rim.
Full score breakdown and sources →
Neither of these is what you own
A comparison is between two product types. The item in your cupboard has its own packaging, its own age and its own condition. Scan it and get the same five-component score for the actual object.
Scan what I actually have