Buying guide

Borosilicate or soda-lime: which glass bakeware to buy, and how to read the one you own

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Two kinds of glass are sold as oven bakeware in America, and only one of them survives a real temperature swing. Borosilicate takes a change of about 330 F before it lets go. Tempered soda-lime takes roughly 100 F. Both are safe for ordinary baking; only one is safe for a frozen dish going into a hot oven. This page lists what is on sale today, sorted by which glass it actually is, and shows how to tell which one is already in your cupboard.

If you want borosilicate: the thermal-shock glass

These are the dishes sold as borosilicate. Borosilicate takes a swing of about 330 F before it lets go; tempered soda-lime takes roughly 100 F. If you pour cold water into a hot dish, this is the group that matters.

American Pyrex today: what the classics actually are

American PYREX (all caps, made in Charleroi and now Lancaster) is tempered soda-lime glass, and has been for decades. That is not an accusation — it is Corning's own published decision. These dishes are fine for ordinary baking. They are not fine for thermal shock.

Pyrex bowls, cups and pie plates (soda-lime, made in USA)

Same glass, same rule. Listed here because the episode gets asked about them every time.

Read the label: manufacturer codes

First 3 digitsBuilt by
PYREX in capitals, inside a circle, with 'CG'Corning Glass Works, 1940s-50s: borosilicate. Keep it.
PYREX in capitals + 'MADE IN U.S.A.'Mid-1950s Corning. Circular logo gave way to a straight line in the 1960s.
pyrex in lowercaseSoda-lime glass. Works fine, but never hot oven to cold or wet surface.
PYREX in capitals + 'Made in France'International Cookware, Chateauroux: borosilicate.
Anchor HockingTempered soda-lime by the company's own statement, not borosilicate.

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