BOSS 136 Fire block /Draft stop Sealant is a one-part, noncombustible filler caulk that is ideal for residential construction and meets all sections of the International Residential Building Code. Formulated for interior use only, it is particularly suited for sealing walls and floors which have been penetrated by pipes, conduits or electrical cables in all types of construction and for filling interior voids around HVAC, plumbing and framing. Having superior adhesion properties, It readily sticks to the most common construction materials and is semi-flexible. BOSS 136 is completely nontoxic and contains no asbestos or PCBs.