Extreme High Temp Sealant is a one-part, non-slumping paste that cures to a rubbery solid at room temperature on exposure to water vapor in the air. This acetoxy cure RTV (room temperature vulcanizing) 100% silicone is designed to perform at temperatures from -85°F (-65°C) to 500°F (260°C), & intermittently to 600°F (315°C).
More info here: EXTREME HIGH TEMP SEALANT INFO PAGE