Durability + Care Our ridged glassware is made from borosilicate glass. Borosilicate glass is completely non-toxic and contains boron trioxide which allows for a very low thermal expansion. Meaning our glassware will not crack under extreme temperatures like regular glass, making our glassware dishwasher safe and safe for all your coffees, matchas, chais, cocktails and more. Stackable Each glass has a ridge on the bottom making them the perfect stack each time. Handcrafted Each glass is hand-blown and handcrafted. Glass is handblown into our custom moulds, while continuously rotating to distribute the glass evenly with the perfect composure of glass and air. Then each glass is placed to properly cool. Then a laser cuts all the ridges and then the base and top rim of the glass is sanded by hand. Finished with our signature "h" on the bottom of the glass. Sizing 3" w x 6" h (set of four) 22 oz