The　thermo-fluidic　characteristics　of　an　ultralightweight　X-type　lattice　cored　sandwich　panel　with　simultaneous　thermal　and　mechanical　load　bearing　capabilities　are　studied　both　experimentally　and　numerically.　Comparisons　with　competing　sandwich　panels　with　periodic　cellular　material　(PCM)　cores　are　carried　out　at　a　similar　porosity　level.　For　a　given　Reynolds　number,　the　highly　porous　X-lattice　cored　sandwich　panel　provides　up　to　38%　higher　overall　Nusselt　number　than　tetrahedral　lattice　cored　sandwich　panel,　while　exhibits　comparable　heat　transfer　performance　to　Kagome　lattice　cored　sandwich　panel.　Although　brazed　joints　between　the　lattice　core　and　the　facesheets　induce　both　transverse　and　longitudinal　vortices,　limited　flow　mixing　as　a　result　of　smooth　mainstream　in　the　X-lattice　leads　to　inferior　average　Nusslet　number　on　both　the　facesheets　and　ligaments　relative　to　tetrahedral　lattice　cored　sandwich　panel.　However,　the　X-lattice　has　a　66%　higher　surface　area　density　than　tetrahedral　lattice,　which　acts　as　the　main　heat　transfer　enhancement　mechanism.　Relative　to　the　reference　ones,　the　X-lattice　cored　sandwich　not　only　provides　an　overall　Nusselt　number　up　to　77%　higher　for　a　given　pumping　power,　but　also　exhibits　evidently　lower　pressure　drop　for　a　given　Reynolds　number.　Therefore,　such　metallic　lattices　fabricated　using　the　simple　metal　sheet　folding　method　are　superior　for　lightweight　thermal　management　systems　where　a　cooling　fluid　with　small　specific　heat　is　driven　by　limited　pumping　power　in　a　long　cooling　channel.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.