dThis article presents a study on Dow Corning(R) XLK(TM), an inorganic porous material with about 50% porosity and a dielectric constant of 2.0. It focuses on matters linked to sealing the porous film by depositing a plasma enhanced chemical vapor deposition (PECVD) dielectric cap layer. The study shows that the material can be modified during cap deposition due to the fast diffusion of reactants and radicals through the porous network, and acquire totally new properties which can be either beneficial or detrimental, depending on the chosen process. In particular, it is found that cap deposition processes on XLK in an oxidizing ambient, as used for SiO2 deposition, should be avoided. On the other hand, a beneficial modification of the dielectric film has been observed after SiC:H capping. It is also shown that there exists a critical thickness of capping material below which the cap layer reveals the presence of pinholes. The critical thickness value for a PECVD SiC:H cap layer on top of an XLK film is around 25 nm.