Types of Glass Storage Containers
Untreated Glass
The cheapest glass to produce is likely all around you: Untreated soda-lime glass is used to make jars, bottles, and cups. If your glass container doesn't say it's tempered or strengthened, it's probably untreated or just regular old glass. But that isn't necessarily a bad thing; for storing food in the fridge or at room temperature, soda-lime glass is fine. It's when you freeze or heat the glass that you want another option.
Tempered Glass
Soda-lime glass can be tempered or heated in such a way that it can withstand a wider range of temperatures.1
How is tempered glass made. Scientificamerican.com.
This tempering process also means that the glass is less likely to shatter. And, when tempered glass breaks, it tends to fracture into small, harmless pieces, not the big, jagged pieces of untreated glass. Tempered glass is not just used in food; car windows, shower doors, and microwave oven doors are made from this material.
Borosilicate Glass
Borosilicate contains boric oxide, which makes it even more resistant to thermal shock than tempered glass, but it's also more expensive to produce. If you're not ready to shell out for borosilicate, don't worry: It usually takes an extreme temperature change, like putting a frozen casserole directly in the oven, for tempered glass to shatter.
