What Is Pyrex?
Pyrex is glass cookware introduced by Corning Glass Works in 1915. The cookware was made with a borosilicate glass marketed as “Nonex.” The company originally developed it for use in railroad lanterns and battery jars to withstand extreme temperatures without breaking.
A company scientist’s wife used Nonex for cooking, and it did not break as her earthenware baking dishes did at high temperatures. The company ran with the idea, and Pyrex was born. Since then, much confusion has arisen due to changes in the product’s manufacturing and branding, as well as in ownership and licensing.
PYREX vs. pyrex
From laboratory glassware to kitchenware, people usually refer to the iconic brand generically. However, there are key differences in the type of glass used to manufacture trademarked “PYREX” and “pyrex” products.
Until some time in the mid-twentieth century, all of the company’s branded glassware was manufactured using borosilicate glass resistant to thermal shock. However, some products manufactured for certain markets, including the U.S., eventually transitioned to soda-lime glass, which makes up about 75 percent of glass production. These are normally branded as “pyrex.”
Though manufacturers often insist that soda-lime glass is just as safe as borosilicate glass, there is some concern that it does not have the same thermal shock resistance. In 2023, the Federal Trade Commission (FTC) also had to remind manufacturers of the famous glassware to be transparent about their “Made in the USA” claims.
At What Temperature Is Pyrex Safe in the Oven?
Avoid heating your Pyrex over 425°F. Further, restrict your use to baking, cooking, or reheating food in a preheated oven.
The best way to determine what temperature Pyrex is safe to use in the oven is to look at the manufacturer’s recommendations. Failure to do so can also void your warranty. If you do not have the original paperwork, try checking the bottom of the cookware for etched safety instructions.
Important Rules To Follow When Using Pyrex
So, can Pyrex go in the oven? Yes, but following the manufacturer’s safety guidelines—as well as common sense—is important. Ways to stay safe and prevent Pyrex from shattering include the following:
Don’t Use Pyrex on Direct Heat
Using Pyrex under a broiler, in a toaster oven, or near a direct source of heat (e.g., an open flame) is not safe.
Let Hot Pyrex Cool Before Refrigeration
As a general rule of thumb, avoid subjecting your Pyrex to extreme temperature changes. If straight out of the oven, let it come to room temperature before transferring it to the refrigerator or freezer.
Let Chilled Pyrex Come to Room Temperature Before Heating
Conversely, if your Pyrex is chilled from the fridge or freezer, let it come to room temperature before putting it in the oven.
Don’t Place Hot Pyrex on a Cool or Wet Countertop
When you remove hot Pyrex from the oven, place it on a cooling rack, wooden cutting board, or other dry, heat-resistant surface. This prevents sudden temperature changes that could shatter the glass.
Preheat Your Oven Before Inserting Your Pyrex
Preheating your oven is a simple but essential step to ensure that your food cooks evenly and to the right temperature. It is also important for using Pyrex safely. Most ovens will indicate when they have reached the desired temperature.
Don’t Introduce Cool Liquids to Hot Pyrex
Adding cool liquids to a hot dish can shatter the glass due to thermal shock. If basting your food, use the heated juices that are already in the pan.
Add Liquid First if Cooking Food That Releases Juices
Fluids released from food while cooking will normally be cooler than the glass. Introducing some moisture beforehand reduces the thermal shock.
Discard Chipped or Cracked Pyrex
Chipped glass is not oven-safe because the structural integrity of the glass has been compromised. Discard chipped or fractured Pyrex.
