We adopt high-borosilicate glass material to produce double wall glass cups, it is lead-free, non-toxic and healthy. A significant function of it is insulation, as holding the cup wall directly with hot water will not feel hot.  There is a vent for all the bottom of cup, which used to discharge the gas during the blowing process, balance the atmospheric pressure of the iner and outer layers to prevent the cup from deforming and bursting. After the production is completed, the hole will be sealed with viscose.