If the recipe calls for baking a food item at 400 degrees, Pyrex glass cookware is safe to use in an oven preheated to that temperature. According to the manufacturer's website, Pyrex cookware -- including measuring cups and mixing bowls -- "can be used for baking in a preheated conventional oven at any temperature that a recipe requires." The products are also safe to use in the refrigerator, freezer or microwave, as long as you follow the manufacturer's use and care instructions.
Pyrex Glassware has been made and sold in America since 1915. The innovation behind the cookware came from the wife of a Corning Glass Works scientist, who wondered if Corning's laboratory glassware would make a better casserole dish than the one she'd been using. The scientist adapted some glassware for his wife's use, and it worked so well that the company developed the concept into a product line for home kitchens.
The original cookware was made using heat-tempered, borosilicate glass similar to Corning's railroad lantern and laboratory glass. This compound is resistant to a wide range of temperatures, but is vulnerable to shattering when dropped or struck. In the early 1950s, Corning began making Pyrex from a tempered soda-lime glass compound that has a comparable temperature resistance but greater resistance to shattering than borosilicate glass. The soda-lime glass has been used consistently since then. Even though styles have changed and innovations added, contemporary Pyrex glassware uses the same formula as the products that were made nearly 60 years ago.
Safe Cooking with Pyrex Ovenware
Always preheat the oven before placing Pyrex cookware in it. While Pyrex is made to go safely from refrigerator or freezer into a conventional, preheated oven, its integrity is at risk when exposed to intense bottom heat or uneven heating. Conventional ovens do not heat evenly during preheating. Until the designated temperature is reached, the actual temperature cycles above and below the setting, and the broiler element or bottom burner is activated. When preheating is completed, the lower burner shuts off and the oven temperature stabilizes, making it safe to introduce the Pyrex glassware and prepared food.
Make sure the bottom of the baking dish is covered with food or liquid. If you are roasting something that doesn't completely cover the dish bottom, such as vegetables or meat, add enough water or cooking stock to evenly cover the bottom before placing the dish in the oven.
Do not place Pyrex glassware under or in direct contact with a heating element or flame. This includes broilers, stovetops, toaster ovens or grills.
Do not use the plastic lids that come with some Pyrex products in the oven. The lids are for storing food in the refrigerator or freezer, and can be used in the microwave as well, but should always be removed for oven baking.
Handle hot glassware with dry oven mitts or potholders, and place it on a dry, heat-absorbent surface, such as a hot pad or folded towel. Make sure the glassware has cooled to room temperature before washing it or putting it in a freezer or refrigerator.