The trademark name for a borosilicate glass that was developed in 1918 for railroad lanterns. It is best known as a line of bakeware that withstands both temperature extremes and rapid changes of temperature that would shatter ordinary glassware.

It also resists chemicals and electricity, and has interesting optical properties, and for these reasons is used in optical applications, laboratory ware, body piercings, and bongs.

You may think you have high-quality borosilicate glass Pyrex brand containers in your kitchen, but probably not.

Borosilicate glass is fiddly and expensive to produce. Back as early as the 1950's Corning discovered they could make their glass cookware using less expensive thermally tempered soda-lime glass. Unfortunately, the soda-lime glass has an issue where it literally explodes seemingly at random when using the glassware for its intended purpose -- to prepare meals and bake. While the expensive borosilicate glass is far superior and does not have this inconvenient explosive shrapnel bomb feature, there are many reports of the soda-lime version causing serious injuries, especially since soda-lime glass shards are quite sharp.

How can you tell which version you have? If your glassware was made in Europe you most likely have the borosilicate version. If your glassware has "pyrex" with a lower-case "P" you have soda-lime glass. If it has a capital "P", it's older glassware and is more likely to be the borosilicate variety. Ballpark is if it was made since the 1980's it's soda-lime glass.

When buying glass bakeware, cookware, and bowls, specifically look for borosilicate glass on the package since it is a selling point. All of my personal glass cookware was inherited from my grandmother (since it is that durable). If you have the soda-lime variety it is important to keep kids and pets away from the kitchen area when using it. The explosions are quite violent and shards are thrown for a distance.

All glassware is susceptible to breaking due to thermal shock. Sticking a glass dish from the oven into a sink full of cold water can cause the dish to break. The difference between how borosilicate and soda-lime breaks is that borosilicate breaks into several large chunks while soda-lime completely shatters into thousands of tiny sharp shards. Removing a roast in a soda-lime baking dish from the oven using oven mitts that are damp or wet can cause the bakewear to explode violently, covering the oven and you with 450-degree glass needles.

What can you do about it? Not too much, if you want to continue using it. Be careful about putting the glassware in positions where there is a large thermal difference. Don't use it on the stovetop, for example. If you like going to thrift stores look for very old Pyrex glassware, or get some imported from Europe if you don't live there.


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