Pyrex products were made of borosilicate glass until the 1950s. At that point, they switched to manufacturing products with tempered soda lime instead. Today, every piece of bakeware made in the U.S. uses tempered soda lime, including the full line of Pyrex consumer glassware.
The brand switched its glassware formula in the 1950s, but has recently reintroduced borosilicate glass into some of its products, such as the Pyrex MealBox™ and Pyrex Hydration line.
I contacted Pyrex to ask if there's an easy way to tell what material your Pyrex dish is made from, and the company had a simple answer: Look at the logo. If it's all caps “PYREX,” it's vintage, made of borosilicate. If it's lower case “pyrex,” it's new, and it's soda lime.
The best way is to look at the bottom of the product. My vintage Pyrex, which is at least 40 years old, and definitely boro-silicate, reads “Not For Lab Or Stovetop Use - Corning N.Y. - U.S.A. - 516 - PYREX.” Newer products made of soda-lime glass do not read Corning N.Y., nor are they made by Corning.
The Pyrex formula changed in 2020. This change was made to make Pyrex glass stronger and better able to withstand temperature changes. The newly formulated Pyrex combines classic trusted heat resistance with improved thermal shock resistance, making it a better choice for glass cookware.
According to the FTC, during the pandemic, Pyrex measuring cups sold on Amazon.com were advertised as made in the United States. In reality, some glass measuring cups were imported from China.
Soda lime glass does not include boron-based components, whereas borosilicate glass incorporates boron trioxide. Soda lime glass, comprised of sodium carbonate, lime, dolomite, silicon dioxide, and aluminum oxide, exhibits lower thermal resistance than borosilicate glass.
Patterned Pyrex—such as the 1956 Pink Daisy or the 1983 Colonial Mist colorways—tend to be valuable as a collector's item. Other popular patterns include the 1957 Butterprint, which features an Amish couple and their crops, and has been valued at a few hundred dollars.
Here's where the branding comes in. All-caps PYREX, which is sold and made in France, is still made of borosilicate glass. But any Pyrex that's all lowercase — a recent change in branding — is soda-lime glass, which isn't designed to withstand drastic temperature changes.
Baking glassware such as Pyrex dishes in usable condition should be donated to local thrift stores or otherwise reused. If unusable they should be thrown away in the trash. They should not be added to curbside recycling. They are made of a different material than glass bottles and jars.
If you're unsure which material your glass kitchenware is made from, you can try eyeballing it to make a rough estimation. Take a close look at the edge of your baking dish, container, or bowl and try to find a bluish-green tinge. If it's there, you've got soda-lime glass. If not, you've got borosilicate glass.
This difference means that Borosilicate glass does not expand as much on heating, so it is less likely to break when heated. Pyrex is one particular blend of Borosilicate glass, with a particularly high heating tolerance.
If it's all caps Pyrex, it's vintage, made of borosilicate. If it's lowercase Pyrex, it's new. And it's soda lime. You still have to be careful.
Corning used borosilicate to produce all Pyrex products. However, the company that purchased the cookware products switched to soda-lime glass, adopting the name pyrex (spelled with all lowercase letters).
It is stronger than regular glass but it can still break or crack if it is dropped or hit hard. It is important to handle borosilicate glass with proper care to minimize the risk of breakage.
Pyrex products were made of borosilicate glass until the 1950s. At that point, they switched to manufacturing products with tempered soda lime instead. Today, every piece of bakeware made in the U.S. uses tempered soda lime, including the full line of Pyrex consumer glassware.
Borosilicate glass is sold under various trade names, including Borosil, Duran, Pyrex, Glassco, Supertek, Suprax, Simax, Bellco, Marinex (Brazil), BSA 60, BSC 51 (by NIPRO), Heatex, Endural, Schott, Refmex, Kimax, Gemstone Well, United Scientific, and MG (India).
Anchor Hocking has been manufacturing tempered soda-lime-silicate bakeware for nearly 40 years. Prior to that time, annealed borosilicate glass bakeware was the standard.
A highly-coveted pattern, the Atomic Eyes Chip and Dip is the holy grail for some Pyrex collectors. Released in the 1950s, some of the bowls feature a Pyrex stamp while others don't.
What Makes Pyrex Special. "Pyrex continues to hold its value because most of us associate it with memories of family and holiday gatherings and memories from their childhood," Wright says. "The vintage designs and patterns of Pyrex evoke a nostalgia, which adds to its value for collectors.
Both trademarks were historically used interchangeably in the marketing of kitchenware products made up of both borosilicate and soda-lime glass. However, now Corning has licensed out the use of their PYREX (upper case lettering) and pyrex (lower case lettering) logos to other companies.
Borosilicate glass is a type of glass that contains boron trioxide which allows for a very low coefficient of thermal expansion. This means it will not crack under extreme temperature changes like regular glass. Its durability has made it the glass of choice for high-end restaurants, laboratories and wineries.
High thermal resistance: Borosilicate glass can withstand temperature changes without cracking, making it perfect for boiling water. Chemical stability: It is resistant to chemical corrosion, ensuring that it does not leach chemicals into the water when heated.
The main differences are the percentage of compounds and the percentage of silica or SiO2 in the glass. Borosilicate is usually in the 80% range, while quartz is over 99%.