The Willi Becher is a traditional beer glass in Germany and the Czech Republic. In the Czech beer culture, thanks to its simplicity and low cost, it has become the most common and widely used pub glass. It is a tall glass, widest about two-thirds of the way up, narrowing both toward the relatively thick base and toward the top rim. The walls are relatively thin, so the beer can warm quickly from the heat of the hands. Another downside is its fragile construction.
The Willi Becher is mainly used for lighter and medium-strength Czech and German bottom-fermented beers.
(taken from the publication "Beer Glassware and Beer Styles – How to Pair," Ondřej Nývlt, Petr Novotný, 2019)
(Note: Compared to typical beer mugs, its walls are thin; however, among beer glasses, the Willi Becher belongs to the more durable ones.)