Silicone Grease offers thermal conductivity.

Epoxies Etc.
Cranston, RI 02921-3407
Jan 02, 2006 Designed to fill wide and narrow gaps, 50-1220 Thermal Interface Material consists of filled silicone grease formulated with combination of filler types. Suited for heat sink and high power applications, one-component product features 0.05% bleed after 24 hr at 200°C, dielectric strength of 210 V/mil, and thermal conductivity of 8 BTU/hr/ft²/in. It is available in 8 oz jars, 16 oz jars, and quarts.