cndota heart shaped double walled insulated glass coffee mugs or tea cups, double wall glass 8 oz - clear, unique & insulated with handle cndota this glassware is made of borosilicate glass that is light and strong. it may feel thin, but it's much stronger and more durable than common glass.</p><p>1.what is it? borosilicate glass is a type of glass with silica and boron oxide. very low coefficient of thermal expansion, resistant to thermal shock.</p><p>2.advantages? *lightweight: borosilicate glass is less dense than ordinary glass. that makes it lighter in weight. *heat resistant: withstanding temperature differentia 165°c /329°f(common glass only 37°c/99°f).perfectly safe for ice drink and hot espresso coffee or tea. *heat preservation: 2-layer design insure that their contents remain hot for longer while the glass itself remains only warm to touch. it also prevents condensation. *more safety : coffee cup is non-toxic, easy clean.</p><p>3.a small spot on the bottom of cup? for the safety of users, it's not vacuum between the 2 layer of mug. to prevent glass pieces blowup and do damage to human when break, our new design mug leave air inside. don't scrub the sealed air hole strongly in washing.</p><p>4.maintenance a. we do not suggest dishwasher, please consider hand washing in flowing water. b. avoid microwave or oven, because of the air inside as mentioned above. </p><p>5.risk free purchase. we're so confident in the quality of product. full refund or replacement will be offered if you're not100% satisfied. click the yellow "add to cart" button now.</p>