Description features:Mouth-blown glasshese,these hand made glasses keep your hot drinks hot and cold drinks cold. The double-walls create a highly effective layer of insulation that reduces heat transfer in or out of the glass. Our double wall cup can be used for everything from drinkware to cookware. Our glass products are all handmade by expert artisans,thus, slight varied on height, thickness & weight could result. Especially double wall structure products? , Please be advance to use care when loading glass with ice cubes since fracturing the inner layer may happen with strong impact. Avoid using metal spoons or placing the glass into a crowded dishwasher. With great cares, Our  glasses will keep hot drinks hot and cold drinks cold for you. For better performance on hot drinks, please pre-heat the glass before use. Borosilicate glass is the formal name of heat-resistant glass, which are widely used on the lab materials to compensate for the extreme conditions.Compares to "soda-lime" glass, borosilicate glass or heat-resistant glass comes with higher costs but wider functionality. With greater demand and popularity, heat-resistant glass has been developed to meet the demands where soda-lime glass can not meet. Borosilicate glass consisted of Boron Oxide and soda, Boron Oxide plays important role to hold soda and lime together with better performance on the index of swell factor also known as coefficient of expansion, in other words, more extreme temperature? tolerated.? Heat resistant glass from EILONG comes with 33.7 on the swell factor which is an A+ grade since markets index of heat resistant glass comes with index of 32 - 50.? With low index figures, Our heat resistant glass stands up to 500 centigrade degrees. Physical property of Borosilicate glass at its best thickness is between 2mm - 2.5mm , which is much thiner compares to soda-lime glass and yet performs even better on the resistant to temperature flunturances and scratching.Borosilicate glass is macrowave and dishwasher safe and remains clear on its color(traditional glass will turn cloudy over time).