Bodum BISTRO Double Wall Thermo-Glass Insulated Mugs, 15.2 oz, Set of 2 Vented!. Used a couple of times, we’ve grown to like hand made ceramic mugs. These award-winning tumblers aren’t just a pretty face; they’re really clever too! Individually mouth-blown from heat-resistant borosilicate glass, our double wall glasses have a thermal quality that keeps hot drinks hot and cold drinks cold. There’s a silicone vent at the base of the glass that equalises the air pressure between the two glass layers when hot or cold liquids are added.