Polyelectrolyte multilayers with alternating porous and fully dense regions have been assembled from poly(acrylic acid) (PAA), poly(allylamine hydrochloride) (PAH), and poly(sodium 4-styrenesulfonate) (SPS) in appropriate combinations. The porous zones were developed postassembly via immersion of the heterostructure film into an aqueous acidic medium followed by rinsing in deionized water. Properly assembled PAH/PAA regions exhibit a reversible, pH-gated nanoporosity transition while PAH/SPS regions remain unchanged upon treatment at low pH. The application of these structures as one-dimensional dielectric mirrors and vapor sensors has been investigated. Organic liquid crystal molecules were also successfully loaded selectively into the nanoporous regions via a capillary force driven wicking action. Potential applications for drug delivery and as Bragg stacks with tunable refractive index layers are also discussed.