JoyJolt double wall glasses are mouth-blown by expert artisans using borosilicate glass. Borosilicate is stronger than traditional “soda-lime” glass and can be used for everything from drinkware to cookware. Due to the natural properties of the boron particles, the glass is held together tighter, resulting in a stronger, lighter glass. Borosilicate glass doesn’t need to be as thick as traditional glass to be just as strong due to the bonding capability boron oxide.