An ultrahigh thermal conductivity (kappa = 160 W m(-1) K-1) of thermal interface materials is achieved with a high enhancement factor (96). A small amount (2.3 vol%) of 1D multiwalled carbon nanotubes (MWNTs) with high. constructs effective phonon transport pathways between microscale silver-flake islands, and a solid phonon transport junction is realized by the coalescence of silver nanoparticles pre-functionalized on the MWNTs.