Pore dimension and transmittance properties of CNT membranes critically determine their efficiency in molecular and ionic transport and separation. These parameters can influence the permeation and molecular discrimination capabilities of the CNT membrane. From Fig. , it can be observed that the pore size of CNT membrane can be tuned by depositing conformal B4C thin films of desired thickness. We note that the 3, 5 and 8 nm thick films reduced the porosity of the membrane from 0.70 to 0.65, 0.60, and 0.52, respectively. This is important for various applications where specific pore sizes are desired. In addition to the inherent tunability of pristine CNT membrane, our conformal B4C deposition process allows a second stage of porosity control. This process allows precise adjustment of membrane thickness, enabling fine-tuning of pore size.