Ü stands for compliance.
And this is we stand for.

In addition to the CE-Marking of our products according to DIN EN 12150-2 und DIN EN 14428, we also attest the adherence to national technical standards as laid down by the German Institute for Construction Technology (‘DIBt’). With the so called Ü-Marking we define thermally toughened safety glass (‘ESG-H’) as per the German Building Rules List A Part 1 Annex 11.11, multiple-glazed insulation glass according to DIN EN 1279 and heat-strengthened glass according to DIN EN 1863.