Polymer　composites　with　excellent　thermal　conductivity,　low　dielectric　constant　and　low　dielectric　loss　are　urgently　required　for　microelectronics　and　wireless　communication　systems.　However,　traditional　thermal　conductive　polymer　composites　realized　by　simply　adding　inorganic　fillers,　cannot　have　high　thermal　conductivity　and　good　electrical　insulation　concurrently,　which　greatly　hinders　the　practical　application.　In　this　work,　a　facile　and　scalable　assembly　technique　to　construct　a　three-dimensional　boron　nitride　foam　(3D-BN)　for　the　formation　of　3D-BN/epoxy　composites　has　been　proposed　to　address　this　long-standing　challenge.　Herein　we　built　a　self-support　and　pressure　reinforced　3D-BN　foam　composed　of　only　bulk-BN　microplates　to　serve　as　the　thermal　pathway.　The　obtained　composite　with　greatly　enhanced　thermal　conductivity　enhancement　(TCE)　exhibits　the　highest　through-plane　thermal　conductivity　of　6.11　W　m−1　K−1　ever　reported　for　bulk-BN　polymer　composites.　Further　analysis　by　finite　element　simulation　revealed　that　the　high　thermal　conductivity　is　attributed　to　the　polymer-free,　pressure　reinforced　3D-BN　foam　which　serves　as　a　more　effective　pathway　for　the　phonons　transmission.　This　work　offers　an　easy　approach　and　provides　a　new　paradigm　for　the　fabrication　and　design　of　thermal　management　polymers.　©　2020　Elsevier　B.V.