The disguise
Glass jar, metal lid — the archetype of plastic-free shopping. It’s what the swap guides (mine included) tell you to buy.
The plastic
Two hiding spots. The airtight seal inside almost every metal twist-off lid is a PVC plastisol gasket — soft PVC that can be ~40% plasticiser, pressed directly against the food. And on crown-capped bottles, the paint on the cap turns out to shed particles into the drink.
The evidence
The gasket problem was documented by Swiss food-control authorities surveying oily foods in glass jars (pesto, vegetables and fish in oil): in one 2005 campaign, 147 of 158 products — 93% — exceeded legal migration limits for plasticisers, with some phthalate readings hundreds of times over (survey summary; related market survey, 2005) agency. EU rules tightened afterwards, but the ring in most closures is still PVC, and oil against lid is still the worst case.
The cap-paint problem is the ANSES 2025 finding that reshaped this site’s assumptions: drinks in glass bottles carried ~100 microplastic particles/L — 5–50× more than plastic bottles or cans — with the particles matching the cap paint, abraded cap-against-cap in storage (ANSES) lab. Full context on the glass page.
The tell — and the fix
The tell: the cream or white flexible ring inside any metal twist lid; painted crown caps on bottled drinks. The fix: buy oily foods (pesto, marinated anything) fresh or make them; store jars upright so contents don’t rest on the lid; look for the small “PVC-free” claim some brands now print; for home preserves, buy lids sold as PVC-free. And hold the hierarchy honestly: a jar with a gasketed lid is still a better container than a plastic tub — this is a footnote to the glass swap, not a reversal of it.