Pyrex Glass

              “PYREX” GLASSWARE

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, lab bottles, 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.


PYREX - group of 3 heat-resistant bowls.

PYREX – group of 3 heat-resistant bowls.

Pictured to the left are PYREX name brand ovenware casserole/mixing bowls. The style or inventory number assigned to this size/type of bowl appears to be “402” as each example has that number embossed on the base, as well as the lettering “TRADE MARK / PYREX / R [in circle] / MADE IN U.S.A. / OVEN WARE”.  Each measures about 7 & 1/4th inches in diameter and 3 & 3/4ths inches in height.  They probably date from the 1970s or 1980s.


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.


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.

Click here to go to the Glass Bottle Marks pages.

Click here to go to my Home Page.

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

12 Responses to Pyrex Glass

  1. Joseph Haley says:

    As an amateur astronomer, I would mention that tons of Pyrex glass has been made into reflecting telescopes mirrors over the years. I have a 10″ , a 15″, and 20″ mirrors in Dobsonian
    telescopes. Most are 2″ thick and weigh up to 60 lbs. They make good telescope mirrors because of their low expansion and contraction with tempature, so that their ground figure does not distort. I belive that Corning still makes the glass availible for this purpose.

  2. E.J. says:

    Soda lime glass has 1/3 the temperature differential of borosiiicate glass, if both are perfectly annealed.

    Soda lime glass has a temperature differential of 99 °F, yes only 99 degrees!!! Pouring very HOT near boiling drippings into the new soda lime Pyrex measuring cups can crack/shatter them

    Borosilicate glass has a temperature differential of 330 °F,
    Pyrex oven dishes are made from this glass, and I hope they are still are. If that $30+ dish of organic lasagna, breaks, the manufacturer is going to get such bad reviews, that out-of-business looms on their failed 5-year plan.

    • Steph says:

      Unfortunately, Pyrex is NOT made from borosilicate glass and has not been for almost 20 years. If an item has a stamp or printed logo in all capital letters, it’s a safe bet that it’s borosilicate. Newer items have the name/logo in all lower case letters, and these are made from soda lime glass.

  3. annette says:

    why does the print come off the measuring cups so fast now ? i had them for years before now the new ones i buy the print comes right off the cup isnt any good with out the meaurments a senior

    • David says:

      Annette, if the print comes off quickly, you might have to buy more cups, and the company sells more product!?? Well, just kidding. I don’t know but I assume the ACL (applied color label) techniques being used on the newer measuring cups are different in some ways than the older type….that is, INFERIOR methods for producing a lasting image. … seems the best ACL graphics were during the 1940s-1960s (such as used on soda bottles, milk bottles, glass sugar and flour canisters, etc). Or maybe that is just a faulty observation of my own that doesn’t hold water.
      Sorry I have no definitive answer. Perhaps a reader can offer more solid feedback on this subject.

    • annette says:

      thank you dear for anwering i always love pryrex and i always used the glass coffee pot for many many years it just broke and im so lost with out it ,i wish they were still making them like years ago .i dont like the new machines they have now i love the smell of perk coffee on the stove .oh well nothing i can do about that now love a senior

  4. Janet Mayer says:

    The glass was not tempered correctly. If you contact the company, I bet they’d replace it for you. The glass would have to be tempered at the factory and there is nothing in the environment that could cause this to happen on a piece of glassware that was tempered adequately. Extreme temps will only impact an untempered piece of glass.

    • David says:

      Hi Janet,
      Yes, proper tempering of glass does REDUCE, but DOES NOT competely ELIMINATE the chance of breakage. There have been hundreds of reports in recent years of this cookware shattering. Such things have happened over the years occasionally, but the frequency of the occurrences have greatly increased after the manufacturers changed their formula to a cheaper grade of glass. SO, whether or not the glass was properly tempered, it is a less durable grade of glass, not as strong and resistant to breakage as the original Pyrex formula was.
      The problem seems to be that the more recently-made Pyrex glass (distributed by World Kitchen) and it’s main competitor brand of cookware (manufactured by Anchor Hocking) are now made of a soda-lime glass instead of BOROSILICATE glass which was the original PYREX formula and which much more resistant to sudden temperature changes.
      From Consumer Reports, quote: “U.S. manufacturers of both Pyrex and Anchor Hocking have switched from borosilicate to soda lime glass for their glass bakeware”
      Please check out these webpages:

      Take care, David

  5. 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.

All comments are moderated, so will not appear on this site immediately. Please, no posts asking about value of an item. I simply don't have the time, energy or knowledge to answer many of the questions submitted here. Some may be answered directly by email, others posted on the site. Thank you for your patience and understanding!

This site uses Akismet to reduce spam. Learn how your comment data is processed.