Technical terms: glass

In itself, glass is of course not a technical term. With a watch, however, glass is not just glass.

In general, every watch glass is about the balance between scratch resistance and breakage resistance. You can (almost) not have both.

• Plexiglas: Hardly scratch-resistant but incredibly break-resistant. Therefore, it is often used in cheaper sports watches. It is incredibly translucent when new (no reflections) but may yellow. The grandpas don't use it.
• Mineral glass: The grandfather's favorite glass. As a specially hardened mineral glass according to Opi's secret recipe, we use it in almost all of our watches. Very scratch-resistant and relatively unbreakable with only low reflection.
• Sapphire glass: This is an artificially produced sapphire and thus the second hardest material in the world after diamond. A great thing in itself, if it weren't for the problem of light refraction and reflection that a sapphire has. This can be greatly improved with a special coating. However, doing this correctly costs a lot of $$$ and is therefore only used by the grandpas when necessary. We have never had a broken glass (at least at the time of publication of this article) - neither with sapphire nor with specially hardened mineral glass.