Double-Wall 12oz Insulated Glass Egg Shaped Mug Teacup with Lid and Filter IDEAL CAPACITY: 12-Ounce; medium volume is perfect for serving tea, coffee, whiskey, juice and others. ELABORATE DESIGN: Durable double layer construction remains cool and prevents condensation. SAFE WASHING: safe for dishwasher and microwave use; not for use with metal utensils TOP QUALITY: made of lead-free borosilicate glass, its heat-resisting and brilliance. Absolutely no air bubble on the walls. WARM REMINDED: There is a small hole in the bottom of the cup, which is the unique trace of the manual blowing process.Not a flaw.