Specular X-ray reflectivity (SXR) was employed to compare structure and barrier properties of a series of nanoporous organo-silicate low dielectric constant (low-k) thin films cured by several different techniques. The polymethylsilsesquioxane films were prepared by curing the same starting material by five different techniques: standard furnace cure, a novel UV light-assisted process, and three plasma-assisted processes. The films' electron density vs. depth profile, pore volume fraction, and moisture uptake were measured by SXR. The measurements illustrate how curing technology can significantly impact low-k film structure and barrier properties and also illustrate the value of SXR for characterization of depth-dependent phenomena in nanoporous thin films. (C) 2004 The Electrochemical Society.