incombustible

/ˌɪnkəmˈbʌstəbəl/
adjective
  1. Not able to be burned; fireproof.
    • This incombustible insulation will not catch fire even in a high-temperature environment.
    • The building's walls are made of incombustible materials like stone and concrete.
    • Firefighters wear incombustible suits to protect themselves from extreme heat.