Thermal interface material: lowest thermal interface resistance or highest thermal conductivity?

Thermal interface materials (TIM) that provide the lowest thermal resistance are critical for the performance and reliability of high performance power devices. Against most intuition, the lowest thermal resistance interface does not generally directly correlate to the highest bulk thermal conductive interface materials. In this video, AI Technology, Inc. illustrates and provides detailed theoretical and practical considerations for using different thermal interface materials in thermal management of high performance electronic devices. For the thermal interface requirements that have controlled flatness, the lowest thermal resistance at 10-30 micron thickness as measured in its configuration are the best predictor of final device performance. COOL-SILVER™ G4 thermal grease in parallel testing is proven to outperform the best of all commercial available thermal greases tested by an independent laboratory. In the case of large areas with less controlled flatness, a patented compressible phase-change thermal pad from AIT is proven to perform close to 100% better and thus increase the life of the electronic device by 2 times when the differential temperature can be as high as 10°C in thickness of 1000 micron (40-mi).
AIT pioneered the use of flexible thermal adhesives and phase-change materials as thermal interface materials (TIM) including thermal pads (COOL-PAD) and the patented compressible phase-change material in the thermal management of microprocessors of personal computers, power converters and supplies. COOL-PAD is a phase-change thermal interface pad material that handles like a plastic sheet but flows and performs like a grease during device operation and shows 200-600% improvement observed in usage.
COOL-BOND is a family of flexible thermal adhesives that provides unparalleled low thermal impedance with proven long-term reliability by not imparting any interfacial bonding stress. These high performance thermal adhesives are available as a thermal paste, thermal film or thermal tape for ease of application. COOL-BOND PSA 3TC is a thermal film that is pressure sensitive to provide instant bond strength of over 100 psi that increases to a bond strength to over 1000 psi with heat on the interface generated by the power components or power modules.
COOL-GELFILM is a film thermal gel that can be applied without mess or spreading into unwanted areas. Once applied, it provides both instant tack and flow to minimize thermal resistance.
COOL-GAPFILL is a compressible high thermal gap pad with outstanding conformal capability to compensate for height differences of components in a circuit module or circuit board to efficiently spread out the heat generated. It is available with one or both sides tacky for different applications.

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Now the better material is pyrolytic graphite sheet