punpun clear coffee mugs set of 2, glass for coffee, double wall insulated glass mugs with big handle, clear mugs each 12.9 ounces,380ml, perfect for americano, latte, cappuccinos and beverage. punpun </p> <p><b> remember: if there's any damage during transit, please contact with punpun directly, we will offer you a new replacement. why is there a hole in the bottom of the clear coffee mug?</b></p> <p><b>the double-layer cup is not vacuum mug. there is an air outlet at the bottom of the outer layer, which is used for the manual blowing process to discharge the gas.</b></p> <p><b>the atmospheric pressure between the inner and outer layers is balanced to prevent the clear mug from deformation and cracking. after the production is completed, the hole will be sealed with glue. (if the mug is vacuum, it will make a loud noise when it’s broken, and it will blow up the glass fragments, which will hurt people easily.)therefore, there is an adhesive hole in the bottom of the clear mug, which is required by the process ,it’s not flawed or defective.</b></p> <p><b> <p><b>please do not wash off the glue on the hole .</b><br></p> </b></p> <p>warm reminder:</p> <p> </p> <p>1. it is recommended to use toothpaste when cleaning stains such as tea or coffee stains .it’s much cleaner and won’t scratch the mug .</b></p> <p><b>2 it is recommended to use a wooden stirring rod to avoid scratches.</p>