A geometrically-structured coaxial cable may prevent infiltration of water vapor and other contaminants by using a closed cell structure. The cable may be fabricated by wrapping bubble tape around its central conductor. Alternatively, plastic may be extruded through channels to create a plurality of layers. In either case, these layers are staggered in a zig-zag pattern to ensure that no radial spokes connect the inner and outer conductors of the coaxial cable without passing through a plurality of dielectric layers.