zangra says

This glass is one of the classic bar glasses because it is handy and fully tempered.
This glass is made of special hardened glass which is shock-resistant and excellently securely stackable.

tempered glass
These glasses are fully tempered and toughened, which makes it extra resistant – five times for resistant than untreated glassware. Tempered glass is economical, resulting in fewer breakages, plus it is safe; when it breaks, it breaks into blunt fragments, to give catering professionals greater peace of mind. Tempered glassware boasts excellent shock and heat-resistance, coupled with exceptional heat-retention levels, provides a glassware that is designed to be long-lasting. Tempered glassware has an increased resistance, but the thickness of the glass is not increased.

Technical description