Boron particles hold together tighter, which results in lighter yet stronger glass. Therefore, your espresso will stay hot, but your hands will stay cool.īorosilicate differs from traditional glass. The double wall is made of heat and condensation resistant borosilicate glass. If you’re into double espressos, this may be what you’re looking for. This double-wall glass espresso mug by Joy Jolt holds a whopping 5.4 ounces.