der Stoff
fabric
A textile fabric or material used to make clothing, curtains, and other things.
Dieser Stoff fühlt sich sehr weich an und eignet sich gut für ein Sommerkleid.
This fabric feels very soft and is well suited for a summer dress.

fabric / material
Loading your saved state.
fabric
A textile fabric or material used to make clothing, curtains, and other things.
Dieser Stoff fühlt sich sehr weich an und eignet sich gut für ein Sommerkleid.
This fabric feels very soft and is well suited for a summer dress.

'Stoff' has many meanings, but they are usually clear from context. Words like 'nähen' (to sew) or 'Kleid' (dress) point to textiles. 'Lernen' (learning) or 'Prüfung' (exam) point to school material. 'Chemie' (chemistry) or 'Substanz' (substance) point to matter.
Ich habe mir einen schönen Stoff für ein neues Hemd gekauft.
I bought a nice fabric for a new shirt.
The plural 'die Stoffe' is used for textiles and chemical substances. For learning material at school or university, however, the singular 'der Stoff' is almost always used, even when many topics are involved.
Im Labor experimentieren wir mit gefährlichen Stoffen.
In the lab, we experiment with dangerous substances.
When 'Stoff' means a textile, it is often combined with verbs like 'kaufen' (to buy), 'zuschneiden' (to cut to size), and 'nähen' (to sew), or adjectives like 'weich' (soft), 'bunt' (colorful), or 'gemustert' (patterned).
Für die Vorhänge brauchen wir einen schweren, dunklen Stoff.
For the curtains, we need a heavy, dark fabric.
In a learning context, 'Stoff' is what you need to know. Typical phrases are 'den Stoff wiederholen' (to review the material), 'den Stoff beherrschen' (to master the material), or 'den Stoff durchnehmen' (to cover/go through the material).
Vor der Prüfung sollten wir den ganzen Stoff noch einmal durchnehmen.
Before the exam, we should go through all the material once more.
When 'Stoff' means the subject matter of a work of art, words from the field of culture often appear. Watch for phrases like 'der Stoff für einen Roman' (the material for a novel), 'ein historischer Stoff' (a historical subject), or 'Stoff für einen Film bieten' (to provide material for a film).
Sein Leben bot genug Stoff für einen spannenden Abenteuerfilm.
His life provided enough material for an exciting adventure film.
Careful: In colloquial speech, 'Stoff' is a widespread term for illegal drugs. This meaning is limited to informal contexts.
Die Polizei ermittelt gegen eine Bande, die mit Stoff handelt.
The police are investigating a gang that deals in stuff.
topic / theme
'das Thema' and 'der Stoff' can both describe what you deal with in a course, text, or work. 'das Thema' is the central subject that people talk or write about. 'der Stoff' means especially the material that you have to know at school, university, or in courses. In art and literature, 'Stoff' can also mean the material for a story. The words can be confused especially when studying: you say 'das Thema der Stunde' (the topic of the lesson), but 'der Stoff für die Prüfung' (the material for the exam) when you mean everything that has to be learned.

Für die Prüfung wiederholt sie morgen den ganzen Stoff aus den letzten Wochen.
For the exam, she will review all the material from the last few weeks tomorrow.
Heute ist das Thema im Deutschkurs eine kurze Bewerbung.
Today, the topic in the German course is a short job application.