In one embodiment, a product includes a plurality of carbon nanotubes and a fill material in interstitial spaces between the carbon nanotubes for limiting or preventing fluidic transfer between opposite sides of the product except through interiors of the carbon nanotubes. Moreover, the longitudinal axes of the carbon nanotubes are substantially parallel, where an average inner diameter of the carbon nanotubes is about 20 nanometers or less. In addition, the ends of the carbon nanotubes are open and the fill material is impermeable or having an average porosity that is less than the average inner diameter of the carbon nanotubes.