Bodum's insulated, double wall glass is handmade by expert artisans. Because this glass is mouth-blown, each one may have slight differences in height, thickness & weight. Please use care when placing ice into the glass to avoid fracturing the inner layer. Please also avoid using metal spoons or placing the glass into a crowded dishwasher. These glasses will help to keep hot drinks warmer and cool drinks cooler. For best results retaining heat, pre-heat the glass before use. Dishwasher & microwave safe.