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"Old" vs. "New" Pyrex

While not necessarily germane to the topic of collectible Pyrex, there is much discussion and debate online regarding the supposed superiority of "old" versus "new" Pyrex.

By old, those who subscribe to this alleged difference in quality mean the borosilicate glass formulation Corning Glass Works first used for Pyrex kitchen glassware beginning in 1915. Those familiar with the origin story know that Pyrex was derived from Corning's Nonex, a type of glass devised to solve the problem of hot railroad lantern lenses breaking when contacted by rain or snow.

By new, they mean the soda lime glass formulation to which Corning would switch its Pyrex consumer kitchen glassware later on.

The topic continues to be dwelled upon online and in the comments section of youtube videos made by "in the know" content creators. More on this later.

All Pyrex kitchen glassware produced and marketed in the US currently, and for quite a long time now, has been made of tempered soda lime glass. It is important to note that Pyrex competitors in the US kitchen glassware market also use soda lime glass.

Borosilicate continues to be used by Corning, Inc. for its labware as it has always been. Overseas, in Europe and other markets, consumer Pyrex is still made from borosilicate.

Corning Divests

In the late 1990s, Corning Incorporated decided to concentrate its resources in areas other than consumer products, where they saw little potential for further growth. The decision was made to focus instead on its labware, its established joint venture Dow-Corning, and moreso on the opportunities seen in the burgeoning fiber optic telecommunications market.

To that end, Corning Consumer Products was spun off, and Borden Chemical as majority stakeholder grouped it together with its holdings Ecko and General Housewares to form World Kitchen, Inc. Bankruptcy reorganization in the early 2000s would result in the entity subsequently becoming World Kitchen, LLC.

Assumptions Made

Through repetition, many have accepted as fact a myth that began circulating after the sale of the consumer products division: that World Kitchen "ruined a perfectly good product", changing the formula from borosilicate and producing Pyrex from cheaper soda lime glass.

The story was further embellished by unfounded claims that World Kitchen moved its production of Pyrex to China.

Backstamp Logo Changes

L-R above: The earliest font seen on Pyrex dishes; the font used mid-20th century; the backstamp used 1950s to early-1970s; the new stylized logo first used ca. 1994 and thereafter.

The myth goes on the purport that one can tell the difference between the "old" and the "new" by the lettering of the word Pyrex in the embossed logo being in all-caps (old, Corning) or in all lowercase (new, World Kitchen).

Never mind the fact that Corning Consumer Products had used the lowercase Pyrex logo as early as 1994.

Some even go further to state that, as opposed to colorless, a bluish or greenish tint to the glass identifies a dish as being the "new" Pyrex.

And, most importantly, the assertion is that the "new" is inferior to the old.

The Change To Soda Lime

In truth, Corning itself changed the formulation of consumer Pyrex from borosilicate to soda lime, and much earlier than the 1990s. In the late 1940s, around the time Corning began to market painted and decorated Pyrex in an opal glass (also a soda lime formulation), clear Pyrex ovenware was also switched to soda lime.

Tempered soda lime glass, like borosilicate, is heat resistant and is perfectly suitable for use as bakeware. It has three benefits over borosilicate:

  • It is more impact resistant.
  • It is less expensive and easier to produce.
  • It is a more environmentally-responsible material in that boron disposal is regulated as hazardous and therefore expensive as well.

Exploding Pyrex?

Nevertheless, in the early 2000s, the internet helped to proliferate and amplify a handful of stories of the supposedly "new" Pyrex spontaneously shattering, laying the blame on World Kitchen for an alledged change to an allegedly inferior material.

Myth-busting website snopes.com even for a time rated the story as "true", apparently based upon a 2008 report by CBS-2 in Chicago, but later reduced the rating to "mixture" when the legitimacy of the TV report was called into question.

Uninformed Sources Chime In

Unfortunately, even nearly a quarter century later, the topic is still being given oxygen by sources who, quite frankly, should know better.

In a short video posted in February 2024, America's Test Kitchen weighed in on the controversy. Although no Pyrex shown in the video is borosilicate, the presenter repeats the same misinformation about upper- and lowercase logos.

Company Literature Provides A Clue

Pyrex use and care instructions have for a long time-- both before and after the acquisition of the brand by World Kitchen-- included these caveats:

  • Always place hot bakeware on a dry, cloth potholder or towel.
  • Never place hot bakeware on top of the stove, on a metal trivet, on a damp towel, in the sink or directly on a counter.
  • Never put bakeware directly on a heat source such as on a stove top, on a grill, under a broiler or in a toaster oven.
  • Always allow the oven to fully preheat before placing bakeware in the oven.
  • Always cover the bottom of the dish with liquid before cooking meat or vegetables.

The above was sourced from the website of World Kitchen, LLC, 2011.

These instructions are from the Corning Glass Works 1953 Pyrex dealer catalog:

Following these simple rules will give a lifetime of service from PYREX Ovenware:

1. Use it in the oven, not on top of the stove or next to flame .
2. When the dish is hot, handle with a dry cloth.
3. Avoid pouring water into hot dish.
4. Avoid placing hot dish on a wet table top, sink, or in water.

Whether or not you believe Pyrex was still borosilicate in 1953, the instructions are basically the same as those in 2011.

Now, let's compare these instructions from the Corning Glass Works December 1937 Pyrex dealer catalog, when Pyrex was still indisputably made from borosilicate:

OBSERVANCE of these simple rules will give a life-time of service from PYREX Brand Ovenware. Use it in the oven not on top of the stove or next to flame. Handle it with a dry cloth while the dish is hot. Avoid pouring cold water into hot dish, or placing hot dish on a wet table top or in water. "PYREX" is a trademark and indicates manufacture by CORNING GLASS WORKS, Corning, New York.

From this we can see that, even in its original composition, borosilicate, Pyrex was potentially subject to breakage from thermal shock. Additionally, the breakage guarantee in the same catalog was limited solely to that occuring while in a heated oven.


So, while it would seem that borosilicate, while superior to soda lime in terms of thermal expansion, is not necessarily impervious to thermal shock.

As of 2024, the last Pyrex ovenware made of borosilicate in the US was produced over 75 years ago. It is safe to say that the chances of encountering any of it today in flea markets, thrift or antique stores are very slim. The shapes of Pyrex made from borosilicate are unlikely to even be recognized as Pyrex by the inexperienced eye.

Do you recognize any of these Pyrex shapes from the 1920s? Probably not.

The best advice is just to use any Pyrex-- be it "old" or "new"-- according to the longstanding manufacturer guidelines, and you'll be just fine.