Glass and ceramic

Glass

Is it plastic?

No, it isn't plastic

Under our published definition of plastic.

Glass is made from melted sand and minerals. It isn't plastic, it doesn't shed microplastics, and it's the easiest material to heat food in. Watch the lids and seals, the decoration on the outside, and sudden temperature changes.

By PlasticFreeHome Research Team · Not yet reviewed by an editor · Updated 26 October 2026

Also called: soda-lime glass, borosilicate glass, toughened glass, tempered glass, crystal
Type: Glass and ceramic
Found in: food storage containers, jars and bottles, bakeware and casserole dishes, baby bottles, drinking glasses, chopping boards
Heat: Excellent heat resistance, but it can crack with sudden temperature changes. Borosilicate copes with these far better than soda-lime glass.
Recycling in the UK: Bottles and jars go in household glass recycling. Drinking glasses, ovenware and broken cookware usually don't: check your council's rules.

What it is

Glass is made by melting sand (silica) with other minerals and cooling it so it sets hard without crystallising. It isn't a polymer, so under our definition of plastic it isn't plastic. Two types matter in the kitchen:

Soda-lime glass is the everyday kind used for jars, bottles, drinking glasses and much toughened cookware.
Borosilicate glass contains boron. It expands about a third as much as soda-lime glass when heated, so it copes far better with sudden temperature changes.

Glass is behind many of our swaps, including plastic tubs → glass, freezer bags → jars and polypropylene baby bottles → glass.

Can glass crack with heat?

Yes. Glass cookware breaks when one part heats or cools much faster than another. A technical review of shattering glass cookware calculated that soda-lime glass can fracture with a sudden temperature difference about a third of the size that borosilicate can withstand. Consumer tests it cites showed soda-lime bakeware shattering when taken from a hot oven and put on a wet worktop.

To avoid it:

Don't move glass straight from the oven to a cold or wet surface, or from the freezer into a hot oven.
Don't add cold liquid to a hot glass dish.
Retire glass that is chipped or scratched.

Does glass release anything?

Plain glass is one of the most stable food-contact materials there is. Two things deserve attention:

Decoration. A study of decorated drinking glasses found lead and cadmium in the coloured enamels, including on the area near the rim. When a selection of these glasses was given a standard acid test, all but one released lead above the limit value. Choose plain glasses, or ones decorated well below the rim.
Lids and seals. Glass containers often come with plastic lids and silicone seals. See glass food containers: the lid problem.

Recycling

Glass bottles and jars go in your household glass collection. Drinking glasses, ovenware, Pyrex-type dishes and crystal are often made from a different type of glass and can contaminate bottle recycling, so councils usually ask you to keep them out of bottle banks. Donate them if they're in good condition, or check your local tip.