Double Walled Insulated Design: The double walled design keeps hot drinks longer while the exterior wall stays cool for hand safe touch. Premium Clear Borosilicate Glass: Made of 100% lead free borosilicate glass, these double walled insulated coffee mugs will provide you the healthiest drinking way. Ideal Size and Volume: These double walled expresso cups are perfectly sized to fit under most at-home brewing stations. Microwave and Freezer Safe: Safe from -30℉ to 150℉, the clear cups have an excellent thermal shock resistance ability.