What it is
Glass is melted sand — silica fused with soda ash and lime, cooled so fast its atoms freeze in place. There is no polymer anywhere in it. Borosilicate (oven and lab glass) adds boron so it shrugs off thermal shock; the everyday jar is soda-lime.
Why it’s safer
The silicon–oxygen network is chemically bound and essentially insoluble at any food temperature or pH — nothing to plasticise, nothing to shed, nothing that softens at 95 °C. When migration scientists need an inert control container to compare plastics against, they reach for glass. That’s about as strong an endorsement as materials science hands out.
The honest caveats
The container is more than the glass. France’s food-safety agency ANSES found glass-bottled soft drinks, iced tea and beer averaged ~100 microplastic particles per litre — 5 to 50 times more than the same drinks in plastic bottles or cans (ANSES, 2025) lab. The particles matched the paint on the metal caps, abraded cap-against-cap in storage; blowing and rinsing caps before sealing cut counts by two-thirds. The glass was innocent. The closure wasn’t. (Glass-bottled water and wine were largely spared.) I’ve made this the site’s standing reminder that “glass = safe” is a habit of thought, not a law.
Jar lids seal with plastic. The airtight ring inside metal twist-off lids is plastisol — plasticised PVC — and its plasticisers migrate into oily foods, especially stored lid-down lab.
Decoration can be worse than the vessel. University of Plymouth testing found lead in the enamel decoration of 52 of 72 drinking glasses (some at the rim, up to 400,000 ppm) and cadmium in 51 of 72 (2017) lab. Plain, undecorated glass sidesteps this entirely.
And the mundane one: soda-lime glass cracks under thermal shock. The realistic everyday hazard of glass is broken glass.
What I do
Glass is my default for storage, blending, cold water and the fridge — the kit is full of it, from the 2 L pitcher to a dozen little jars with bamboo lids. I buy plain over printed, store oily jarred food upright, and treat painted-cap bottled drinks as no better than their plastic-bottled neighbours until proven otherwise.