Happy Sales Set of 6 Double Wall Insulated Glass Teacup Coffee cups Tumblers 6 oz, Clear Happy Sales double wall cups measuring 3"D x 3.25"H and holding 6 oz. Mouth-blown, lab-quality borosilicate-glass construction; durable and heat resistant. Material: Heat-resistant Borosilicate glass (-20 DegreeC -- 150 DegreeC) Set of 6 cups. Double wall keeps drinks hot or cold. Dishwasher safe but Hand wash recommended.