durchsichtig
transparent
Made in such a way that you can see through it; transparent. Light can pass through the material largely unhindered.
Die Wasserflasche ist aus durchsichtigem Plastik.
The water bottle is made of transparent plastic.

transparent
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transparent
Made in such a way that you can see through it; transparent. Light can pass through the material largely unhindered.
Die Wasserflasche ist aus durchsichtigem Plastik.
The water bottle is made of transparent plastic.

The adjective is made up of 'durch' (through) and 'sichtig' (from 'Sicht', view/sight). So it literally means that a view 'through' something is possible. This logic applies to both the concrete and the figurative meaning.
Das Fenster ist so sauber, es ist fast unsichtbar.
The window is so clean, it's almost invisible.
Whether the literal or figurative meaning is intended depends on the noun. If the adjective describes a material or object, it is meant literally. If it describes an idea, an action, or a statement, it is meant figuratively.
Seine Argumentation war nicht sehr überzeugend und ziemlich durchsichtig.
His argument was not very convincing and quite transparent.
In the literal meaning, 'durchsichtig' (transparent) is often combined with materials. Typical examples are 'durchsichtiges Glas' (transparent glass), 'durchsichtige Folie' (transparent film), or 'durchsichtiges Wasser' (clear water).
Die Dokumente sind in einer durchsichtigen Hülle geschützt.
The documents are protected in a transparent sleeve.
In the figurative meaning, 'durchsichtig' (transparent/obvious) usually describes abstract things. Common combinations are 'eine durchsichtige Lüge' (a transparent lie), 'ein durchsichtiger Plan' (a transparent plan), or 'ein durchsichtiges Manöver' (a transparent maneuver).
Sein Versuch, uns zu täuschen, war ziemlich durchsichtig.
His attempt to deceive us was quite transparent.
clear
'klar' and 'durchsichtig' can both describe that you can see through a material. In this sense, they are very similar. 'durchsichtig' states this quality very directly and fits with glass, plastic, film, or fabric. 'klar' sounds especially natural with water, glass, air, or visibility, and can also mean that something is not cloudy. Learners may confuse the words because both mean 'you can see through it'. But pay attention: 'klar' has many other meanings, for example 'understandable', while 'durchsichtig' mainly describes the visible property of a material.

Im Supermarkt sucht der Gast eine durchsichtige Tüte für das Obst.
At the supermarket, the customer looks for a transparent bag for the fruit.
Das Wasser im See ist heute so klar, dass man die Steine sieht.
The water in the lake is so clear today that you can see the stones.