Pyrex Glass


Corning Glass Company/Corning Glass Works, Corning, New York (1875-to date).     (Now known as Corning Incorporated).

The trademark “Pyrex” was first used c. 1915 for Corning’s borosilicate heat-resistant glassware formula.  VERY large quantities of kitchenware, serving bowls, ovenware, measuring pitchers, etc, as well as glass electrical insulators for telephone and power lines were made.

Pyrex ovenware has been a staple in American households for many decades.

Bottles and other types of heat and chemical-resistant laboratory glassware are also found with the “PYREX” name embossed on the bottom.    Glass tubing, test tubes, funnels and other miscellaneous laboratory equipment and containers were made in quantity.

CD 233 style power line insulator. Marked "PYREX  REG. U.S.PAT.OFF. // 661 / CORNING MADE IN U.S.A."

CD 233 style power line insulator, circa 1930s or 1940s.  Marked “PYREX REG. U.S.PAT.OFF. // 661 / CORNING  MADE IN U.S.A.”


Some “Carnival glass” insulators were made, bearing the PYREX / CORNING brand marking.     The most common Pyrex insulator (found in clear glass) would probably be the CD 128 style.  A search of the internet, such as Google Images pages with  “Pyrex insulator”  and “CD 128″ should bring up examples of that particular shape.

NOTE: In 1998, Corning discontinued the production of their PYREX line of glassware, (concentrating instead on their lines of tech-related products) and the rights to the PYREX brand name was assigned to World Kitchen, LLC.   The  original formula for the glass was evidently changed after 1998, to a  tempered soda-lime glass, and there have been complaints by consumers that this recently-made glassware (ovenware, etc) has shattered and appears to be inferior to previous standards of durability characteristic of the earlier borosilicate formula.

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For more detailed information on Pyrex glass, check Wikipedia’s webpage here.

2 Responses to Pyrex Glass

  1. L Cross says:

    I had a Pyrex 4 cup measuring cup explode in my cupboard.I have had it for only about 8 months. What would have caused this?

    • David says:

      I don’t know, but assume it is a more recent, perhaps poorly annealed / lower quality glass. Even Pyrex can break if subjected to sudden EXTREMES of heat and cold within a short period of time.