OGGI's Borosilicate Glass Espresso Cups Set will suspend your espresso and crema within an inner crystal clear insulated glass wall for an engaging optical effect. The double wall construction of the glass in this heavy duty espresso coffee mug set allows for high heat retention properties with a cool-to-the-touch exterior. A beautiful way to enjoy an espresso longer or showcase your barista crafting. Oggi's double wall glasses are scratch and temperature resistant and can withstand temperature swings that can shatter or crack normal glassware. Oggi's double-walled glass is essentially a glass within a glass. The air between the two glasses is sucked out when it is made, creating a vacuum. It is designed to keep beverages at the correct temperature by not allowing heat to escape or enter.