Uniweld’s 91861 Cool Blue™ Heat Sink Paste protects rubber and plastic seals in ball valves, solenoid valves, reversing valves and heat sensitive materials. To prevent overheating: a heat transfer indicator has been added to the paste. When exposed to heat, the paste will change to a dark blue. Safe to use, non-toxic, harmless to skin and odorless. Easy to clean; simply wipe off with cloth or wash with water.