Nu-Calgon 4371-36 Thermo-Trap®

Technically, Thermo-Trap is referred to as a heat sink. This means that it has an extremely high capacity for absorbing heat. Applied to the metal working surface between the area being heated and the material to be protected, Thermo-Trap soaks up heat and reduces heat transfer. This keeps heat from spreading beyond the work area. Heat-sensitive components, installed fittings, etc., on the other side of Thermo-Trap stay cool and are not damaged by transmitted heat.
Apply to copper, steel or other pipe surfaces before welding, brazing or soldering to protect nearby sensitive controls or components. Protect adjacent surface areas from over-heating or damage prior to welding, brazing or soldering. Use to cool down heated surfaces.

This product must be used in accordance to the following directions by HVACR professionals only.
Before you solder, braze or weld, squeeze a collar of Thermo-Trap Paste around the metal work surface between the area being heated and the material to be protected. The amount required will vary depending on the thickness and heat-conducting properties of the metal being worked, the temperature of the heating tool, and the length of time heat is applied. Your own experience will be the best guide in deciding how much to use. Remember, too much Thermo-Trap can’t hurt. Too little could. Be sure Therno-Trap contacts the metal surface closely all around and there are no pockets or voids where heat might transfer through. After the job is done, just rinse off with plain water or wipe off with a damp cloth.