NuFlex¨ 800 High Temperature Latex Sealant is an easy to apply sealant for gas burning systems such as gas appliance venting, fire box area of direct vent gas fireplaces, hot gas ducting, and piping flanges. It is designed to withstand 800 degrees F continuously. NuFlex¨ 800 resists vibrations, cracking, fumes, gases, moisture and acids formed by gas combustion by-products. It will not shrink over time nor when heated. Black. Comes in a 10.2 oz tube that fits most standard caulking guns.