slow-burning

adjective4

1. •
   Which burns more slowly than comparable objects.
2. •
   Emerging or unfolding slowly or gradually.

   • When the Missouri-born 26-year-old released her debut album last September, it marked the beginning of a slow-burning second act in pop. — 2024
3. •
   Of a song; that relies on anticipation and steady momentum; characteristically may be sparse or atmospheric.

   • "Neon Gravestones" is a forlorn, slow-burning hip hop piano ballad.
4. •
   Made of material designed to resist fire.