"eGRAF HR-400 Heat Riser components are ideal for confined heat sources or ruggedized, sealed systems. Made from natural graphite (400W/m-K Thermal Conductivity) heat riser is mounted between the chip and heat sink to improve the heat flow from sensitive components to external casing."
FULL STORY @ GRAFTECHAET (http://www.graftechaet.com/eGRAF/eGRAF-Products/HR-400-Heat-Risers.aspx)