1. What does it mean?
재질 ordinarily refers to material or its qualities. In casual online descriptions, ~재질 can instead mean that someone or something gives a particular impression: a lead-character vibe, a certain mood, or the kind of thing that fits your taste.
Also written or said as jaejil
2. The nuance
This use is figurative rather than a statement about physical fabric. It can be admiring, humorous, or descriptive, so the noun placed before 재질 supplies much of the meaning.
3. Examples
“이 노래는 새벽 산책 재질이야.”
This song has late-night-walk vibes.
“주인공 재질이라는 댓글은 실제 배역이 아니라 분위기를 말한 거야.”
The 'main-character material' comment was about the person's vibe, not an actual role.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.