Abstract: Porous materials such as 5A molecular sieve (5A) display huge thermal resistance due to high porosity and lots of voids between grains that is negative to hydrogen isotope separation engineering. Generally, introducing thermal conductive fillers contributes to reducing thermal resistance while results in decreasing volume ratio of porous materials and then certainly causes declined hydrogen adsorption capacity. Here, a liquid polydimethylsiloxane (PDMS) is pressed into the voids between 5A grains, which is further developed into a silicon, oxygen and carbon (SiOC) structure suffering from 350 C sintering. 5A/SiOC composite at 10 wt% polydimethylsiloxane (5A/SiOC10) displays 0.74 W/mK of thermal conductivity, which is about 300% higher than that of neat 5A. More importantly, enhanced rather than reduced hydrogen adsorption capacities at a fixed volume of the composite are determined. 5A/SiOC10 shows adsorption capacities of H2 (175.4 mL/ cm3) and D2 (188.4 mL/cm3) while neat 5A shows that of H2 (171.6 mL/cm3) and D2 (165.8 mmol/cm3) at 77 K with 1 bar. Besides, enhanced thermal conductivity of porous materials shortens the cycle time of hydrogen isotope separation that contributes to reducing energy consumption. This work proposes a novel strategy on void filling to tailor thermal resistance of porous materials, which open a window to improve hydrogen isotope separation with thermal management materials.