Happy Sales Double Wall Insulated Glass Coffee Mug Teacup, 12 oz, Clear Happy Sales double wall mugs measuring 3.5"D x 4.5" H and holding 12 oz. Mouth-blown, lab-quality borosilicate-glass construction; durable and heat resistant. 2-layer design creates dramatic optical illusion and prevents condensation. Double wall keeps drinks hot or cold. Dishwasher safe but Hand wash recommended.