There are several types of glass that you can use for your bed -- and several types of glass in general. Let's start there:

Types of glass

Not all glass is created equally. There are 3 main types of glass. Windows, glass jars, and lab equipment all use different types of glass with different properties.

Glass Type Thermal Shock Resistance* Chemical Resistance Applications Soda-lime silicate Low Average Food and beverage containers, windows, lamp envelopes Phosphates Low Low, except for hydrofluoric acid Bone scaffolds, optical fibers, heat absorbers Borosilicate Average-High High Industrial equipment, exterior lighting, laboratory and kitchen glassware

*Thermal shock resistance

Thermal shock resistance is an important property to consider when choosing a glass for your bed. It is essentially the ability of a solid to withstand sudden changes in temperature during heating or cooling.

Thermal shock resistance is the ability of a solid to withstand sudden changes in temperature during heating or cooling.

Your glass bed will rapidly cool or heat when your heated bed is activated, when the extruder comes into close contact with the print surface, or when a print finishes in a cold environment. Therefore, it's important that your bed not explode with sudden temperature changes.

Additionally, cheap glass like soda-lime silicate can contain bubbles; when this glass is heated, the air in these bubbles can expand and shatter the glass.

Go with borosilicate

Borosilicate glass is the same type used in labs for beakers and other neat labware. There's a reason scientists choose this type of glass: it's highly resistant to temperature changes and chemicals. It's consistently smooth and flat and doesn't contain bubbles that can cause the glass to fracture or explode while heating.

You probably shouldn't have Home Depot cut your bed for you

Some people have cut inexpensive soda-lime silicate glass panes or IKEA mirrors to size for use on their printer and have experienced success for some time with them; this doesn't mean that they're safe to use, nor does it mean that they will last a long time.

tl;dr; Use borosilicate glass. A proper borosilicate glass bed is very inexpensive (more on that later).