All Pyrex is made of tempered glass, which is engineered to be tougher than regular glass. If it breaks, it's also designed to shatter into tiny, less-dangerous pieces, like a car windshield.
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.
PYREX® is a borosilicate glass from CORNING with excellent thermal properties. A low expansion coefficient of only about one-third of that of soda-lime glass materials ensures high thermal shock resistance. PYREX® material has been used to manufacture temperature-resistant optics for a long time.
It's tempered, meaning it's been heated and cooled in a manner that makes it more durable under future temperature fluctuations. It's less likely to break under an impact, and when it does, tempered glass breaks into diamond-like cubes instead of long, pointy shards, so it's a little safer to deal with.
According to Pyrex's safety and usage instructions, “While the glass is designed for temperatures typically used in baking, it can break when exposed to the direct heat element while the oven is preheating.”
All Pyrex is made of tempered glass, which is engineered to be tougher than regular glass. If it breaks, it's also designed to shatter into tiny, less-dangerous pieces, like a car windshield.
Pyrex eventually switched to tempered glass most likely because boron is toxic and expensive to dispose of. Although tempered glass can better withstand thermal shock than regular soda-lime glass can, it's not as resilient as borosilicate. This is what causes the shattering reaction people are talking about.
The maker of Pyrex glassware and Instant Pot multicookers has filed for bankruptcy protection, with as much as $1bn (£790m) in liabilities. Instant Brands blames high interest rates and weak demand for its problems. The company, which has more than 2,400 workers, plans to keep operating while it shakes up the business.
Because borosilicate is the most durable when it comes to withstanding temperature changes, it is generally considered the safest choice for glass bakeware.
The effects of thermal shock are great and can cause the glass to break. Even pyrex (like Pyrex) can break when improperly poured boiling water. To prevent the glass from breaking when exposed to boiling water, sudden and drastic temperature changes should be avoided.
On the other hand, tempered glass is stronger and more impact-resistant than borosilicate glass, making it a safer option for certain uses. Another difference is in how they break.
Unfortunately when Corning, Inc. sold off the PYREX® trademark it became pyrex® in America and the new company started using Soda-Lime Glass instead of Borosilicate Glass. The company that bought the PYREX® trademark for European use continues to make Borosilicate Glass PYREX.
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.
Tempered Soda Lime. The various formulations for Pyrex glass have been a source of controversy for many, as well as a source of consumer lawsuits over shattering bakeware.
In the U.S., modern Pyrex cookware is made from a type of tempered glass called soda lime glass, which isn't nearly as durable as the glass used in older pieces called borosilicate. Incredibly tough, borosilicate has one especially notable superpower: the ability to endure sudden shifts in temperature.
DO NOT use or repair any glassware that is chipped, cracked or severely scratched. DO NOT drop or hit glassware against a hard object or strike utensils against it. Pyrex® Glassware can be used for cooking, baking, warming and reheating food in microwave ovens and preheated conventional or convection ovens.
So What's the Difference? The short answer is: not that much! Both brands can go into the oven up to 425 degrees F (200 degrees C), recommend using trivets when moving from hot to cool surfaces, and come in a variety of shapes and sizes at affordable prices. It really just depends on which one you like more.
This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly.
Corelle Brands is home to iconic, category-leading brands, including Instant™, Corelle®, Pyrex®, Corningware®, Snapware® and Chicago Cutlery®. We're passionate about delivering products that facilitate the joy we find in cooking and sharing food with family and friends.
The brand switched its formula in the 1950s to the soda lime glass, but recently started reintroducing borosilicate glass. Although both glasses are heat-resistant, borosilicate glass does better with extreme temperatures, making the vintage Pyrex pieces highly coveted by collectors.
The Bottom Line
Pyrex: Brand name for cookware brand. pyrex: Lowercase indication of containers that should not be heated in the oven or microwave. These are most likely made of soda-lime glass. PYREX: Uppercase label on cookware that is made of borosilicate glass and can be heated in a microwave or oven.
More than 100 years later, the brand has evolved from glass bakeware into other glass products that include food storage, serveware, drinkware, mixing bowls, and more. Anchor Hocking glass bakeware is made with tempered soda-lime glass, giving it durability and heat resistance.
The USDA Food Safety and Inspection Service has deemed Pyrex as microwave safe. There are some things you need to know though! Pyrex is made of either borosilicate or soda lime glass and is heat resistant up to 425 degrees Fahrenheit, making it a good option for microwaving.