
gläsern
made of glass
Consisting of the material glass.
Der Konferenztisch war modern und komplett gläsern.
The conference table was modern and completely made of glass.
glass / transparent
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made of glass
Consisting of the material glass.
Der Konferenztisch war modern und komplett gläsern.
The conference table was modern and completely made of glass.

transparent
In a figurative sense, transparent, see-through, or easy to monitor. Often used to describe a lack of privacy.
Durch die umfassende Datensammlung wird der Bürger immer gläserner.
Through extensive data collection, citizens are becoming increasingly transparent.

fragile / cold
Figuratively, fragile, brittle, or lacking emotional warmth.
Nach dem Streit herrschte ein gläsernes Schweigen zwischen ihnen.
After the argument, a cold, fragile silence hung between them.
The adjective 'gläsern' (made of glass/glass) is derived from the noun 'das Glas' (glass). The ending '-ern' is often used to describe a material something is made of.
Die gläserne Vase zerbrach in tausend Stücke.
The glass vase shattered into a thousand pieces.
In the figurative meaning 'durchschaubar' (transparent/see-through), 'gläsern' (transparent) is often used in socially critical contexts. A very common phrase is 'der gläserne Bürger' (the transparent citizen) or 'der gläserne Mensch' (the transparent person), used to describe the loss of privacy through data collection.
Viele Menschen fürchten sich davor, zum gläsernen Bürger zu werden.
Many people are afraid of becoming transparent citizens.
The meaning 'zerbrechlich' (fragile) or 'kühl' (cold) is usually recognized in connection with emotions or moods. Typical examples are 'ein gläsernes Lächeln' (a fake, fragile smile) or 'gläsernes Schweigen' (a cold, tense silence).
Sie gab ihm nur ein kurzes, gläsernes Lächeln.
She gave him only a brief, fragile smile.
transparent
Both words can express openness and the absence of concealment. Transparent usually describes clear, understandable processes or information, whereas gläsern places more emphasis on people losing their privacy and being easy to monitor. Use transparent for understandable procedures and gläsern for a critically perceived lack of privacy and monitorability.

Durch die ständige Überwachung fühlen sich viele Bürger gläsern.
Many citizens feel constantly watched because of the ongoing surveillance.
Die Stadt erklärt transparent, wie sie das Geld für das neue Projekt verwendet.
The city clearly explains how it is using the money for the new project.