Cool Blue Heat Sink Paste Paste protects the rubber and plastic seals in ball valves, solenoid valves, reversing valves and heat sensitive materials. To prevent overheating: a heat transfer cool indicator has been added. As paste absorbs heat, it changes to a dark blue. Safe to use, non-toxic, harmless to skin and odorless. Easy to clean: wipe off with cloth or wash with water. Shipped in units of twelve.