No chance of a mix-up- this not only applies to the individually decorated glasses but the POLAR series as a whole as well. Its playful design is unique, and at the same time, it scores with an extremely practical side effect that prevents the handmade glasses from being mistakenly switched among the guests present. Each one is also made of non-breakable, heat-resistant borosilicate glass - also known as Jena glass - which was developed as early as 1887 by the German chemist and glass technician Otto Schott. Jena glass currently experiencing a true renaissance. The tradition of this ingenious inventor united in new garb.