TherMix is a ready-mix, Vermiculite-based masonry material. TherMix cures into a lightweight, semi-hard mass that forms a thermal insulation barrier to keep flue gases warm and exterior chimney surface temperatures within safe limits. Additionally, TherMix acts as a masonry filler. When poured into the masonry chimney, TherMix fills voids and cracks this eliminates airflow and moisture build-up between the liner and chimney. Listed by Underwriters Laboratories (UL), UL 1777, in combination with several brands and types of lining materials for use in applications where chimneys are in direct contact with framing or other combustible materials (Zero Clearance). *NOTE: TherMix by itself is not a chimney liner. Installation instructions provided by the liner manufacturer must be followed.