A novel method for studying the penetration of wet chemicals into caulked and uncaulked porous dielectrics was developed, and the barrier properties of parylene X were evaluated. Rutherford backscattering spectrometry (RBS) was used to study the penetration of chlorine-tagged organics, 3-chloro-1-propanol and a %5 HCl solution. After one minute of exposure time, eight times more 3-chloro-1-propanol diffused through uncaulked porous dielectric compared to caulked porous dielectric. Penetration from the side of the samples was found to be insignificant.