Boss or Metacaulk fire caulk. Used as a flame fire stop for interior use. General purpose sealant for use on through-penetrations for both horizontal and vertical surfaces. It is a single component, no-sag, water based sealant that is easy to apply and clean up. It cures to a flexible seal that is suitable for conditions where dynamic movement is expected. It bonds quickly, has excellent adhesion and is non-toxic. 10 FL. OZ.