Borosilicate Glass vs Soda Lime Glass

All glassware used for food prep and storage is non-toxic regardless of the type of glass used to make it. The three common types of kitchen glassware are borosilicate glass, soda-lime glass, and tempered soda-lime glass.

In the table above we have summarized the characteristics and uses of the different kinds of glass used in the home kitchen and pantry. Together with that information, it is also important to read and follow the safety and use guidelines usually included with the product description.

Pyrex “Exploding”

You may have read stories or product reviews about glass cookware that suddenly shatters or breaks. If accompanied by a loud noise and flying fragments it becomes an explosion to the startled witness.

While it can be frustrating to not know how these incidents happened, especially when you are eyeing a potential product, it is also important to know that they are circumstantial and can potentially be avoided with the right knowledge about the various types of glass and their purpose.

“When compared to the millions of glass cookware items that are in use in consumers’ homes, the number of incidents is small and the risk is low.”

The rare phenomenon of glassware suddenly “exploding” is usually due to manufacturing imperfections or surface damage. Surface damage can result from any mistreatment of glass, such as repeatedly dropping it on the floor or banging it against another item.

Sometimes this type of damage is unseen but can weaken the glass without fully breaking it. For example, if you drop glass kitchenware on the floor but it doesn’t break, be mindful that the impact may cause it to suddenly shatter in the future if it experiences a sudden temperature change or is bumped against something else that is hard.

Several cases of exploding glass have been investigated since 2014. One glass expert said that glass is durable only if it’s made correctly; impurities and shaping flaws were usually the main culprits behind unexpected shattering. Such flaws can cause uneven heating of the product, leading to greater or lesser heat concentration in a specific part of the glass.

Patty Davis, Deputy Director of Communications and Press Secretary for the Consumer Product Safety Commission noted: “When compared to the millions of glass cookware items that are in use in consumers’ homes, the number of incidents is small and the risk is low.”

What is borosilicate glass?

Borosilicate glass is made by combining silica (quartz sand), boron oxide, aluminum, and zinc. Borosilicate glass is non-toxic and is highly resistant to thermal shock and extreme temperature changes. It is commonly used in making cooking pots and baking dishes.

There is currently (since the late 90s) no Made in USA borosilicate glass cookware; it’s all imported.

Under normal service, borosilicate glass can withstand temperatures from -40°F to 446°F. With such a wide temperature range you can use this glass in preparing meals from freezer to oven to table without worrying about shattering due to sudden temperature change. Borosilicate glass is also shock-resistant, however, it can still break when the impact is really strong. When this type of glass shatters, it breaks into large or chunky pieces.

Soda-lime glass

The two types applicable to kitchen and pantry use are tempered soda-lime glass and regular soda lime glass. Both are made of silica, soda (sodium oxide), lime (calcium oxide), and a bit of aluminum oxide. An oxide is an element that is combined with oxygen.

Tempered soda lime glass is basically a toughened soda-lime glass. Its tempering process makes it up to 5 times stronger than standard soda-lime glass. In addition, it can resist temperatures of up to 428°F which is why it is widely used in making glass cookware and bakeware. All Pyrex glassware currently made the US is tempered soda-lime glass. The switch from borosilicate was made in the 1990s due to boosting the ability of tempered soda-lime glass to resist impact when dropped.

Tempered soda-lime is commonly labeled as “safety glass” because when it shatters, it turns into dull-shaped granular pieces – making it less likely to create injuries. However, it’s not as thermal shock resistant as its borosilicate counterparts and is more sensitive to  sudden, extreme temperature changes. Tempered soda-lime is perfectly fine for most household kitchen applications.

Regular soda-lime glass is the most commonly used glass material for kitchen use – glass containers, food jars, beverage bottles, and so much more. While it can be heated, this type of glass can only safely withstand up to 230°F and a sudden temperature shock of 40°F. Out of the three types of glasses, you need to be most careful with regular soda-lime glass. When it shatters, it breaks into sharp or jagged shards.

Recycling glass

The most recyclable type is regular soda-lime glass. While it is possible to recycle both tempered soda-lime and borosilicate, it would be uneconomical since they need a special facility due to their composition.

Nevertheless, all three types can be recycled by reusing them. For example, you might want to use a glass baking dish with chipped handles as a cutlery organizer. The chips can be sanded with a nail file or sandpaper to make them smooth and safe to handle.

In the US alone, there are 44 glass manufacturing plants operating in 21 states and 63 glass processing plants in 30 states. Recycled glass products are cleaned and sorted, then resold to manufacturing companies for remelting into new food and beverage containers and other products that use glass such as insulation.

Using glass kitchen products is safe and eco-friendly. If your top priority is recycling and sustainability, then using regular soda-lime is ideal. If, on the other hand, your prime concern is using products that can handle dramatic temperature changes (e.g., oven to cold marble countertop), then borosilicate or tempered soda-lime glass are the safer choices.

Although glass can shatter, it’s quite rare that it happens from temperature changes alone if you use the right type of glass and always stay within the recommended temperature range indicated in the manufacturer’s instructions.